Novelty of Carbon Dioxide and Rascality of Carbon Monoxide

By: Dr.Badruddin Khan

Carbon Dioxide is a colorless, odorless, and slightly acid-tasting gas, sometimes called carbonic acid gas, the molecule of which consists of one atom of carbon joined to two atoms of oxygen (CO2). It was called “fixed air” by the Scottish chemist Joseph Black, who obtained it through the decomposition of chalk and limestone and recognized that it entered into the chemical composition of these substances. The French chemist Antoine Lavoisier proved that it is an oxide of carbon by showing that the gas obtained by the combustion of charcoal is identical in its properties with the “fixed air” obtained by Black. Carbon dioxide is about 1.5 times as dense as air. It is soluble in water, 0.9 volume of the gas dissolving in 1 volume of water at 20° C (68° F).

Carbon dioxide is produced in a variety of ways: by combustion, or oxidation, of materials containing carbon, such as coal, wood, oil, or foods; by fermentation of sugars; and by decomposition of carbonates under the influence of heat or acids. Commercially, carbon dioxide is recovered from furnace or kiln gases; from fermentation processes; from reaction of carbonates with acids; and from reaction of steam with natural gas, a step in the commercial production of ammonia. The carbon dioxide is purified by dissolving it in a concentrated solution of alkali carbonate or ethanolamine and then heating the solution with steam. The gas is evolved and is compressed into steel cylinders. The atmosphere contains carbon dioxide in variable amounts, usually 3 to 4 parts per 10,000, and has been increasing by 0.4 percent a year. It is used by green plants in the process known as photosynthesis, by which carbohydrates are manufactured.

Carbon dioxide is used in the manufacture of sodium carbonate, Na₂CO₃· OH₂O (washing soda); sodium bicarbonate, NaHCO₃ (baking soda); and basic carbonate of lead, Pb₃ (OH)₂(CO₃)₂ (white lead). Dissolved under a pressure of 2 to 5 atmospheres, carbon dioxide causes the effervescence in carbonated beverages. Carbon dioxide does not burn and does not support ordinary combustion, and because of these properties it is used for extinguishing fires. The CO₂ extinguisher is a steel cylinder filled with liquid carbon dioxide, which, when released, expands suddenly and causes so great a lowering of temperature that it solidifies into powdery “snow.” This snow volatilizes (vaporizes) on contact with the burning substance, producing a blanket of gas that cools and smothers the flame. Solid carbon dioxide, known as dry ice, is widely used as a refrigerant. Its cooling effect is almost twice that of water ice; its special advantages are that it does not melt as a liquid but turns into gas, and that it produces an inert atmosphere that reduces bacterial growth. The presence of carbon dioxide in the blood stimulates breathing. For this reason, carbon dioxide is added to oxygen or ordinary air in artificial respiration and to the gases used in anesthesia.

Carbon Monoxide is a chemical compound of carbon and oxygen with the formula CO. Carbon monoxide melts at -205°C (-337°F) and boils at -191.5°C (-312.7°F). It is a colorless, odorless gas, about 3 percent lighter than air, and is poisonous to all warm-blooded animals and to many other forms of life. When inhaled it combines with hemoglobin in the blood, preventing absorption of oxygen and resulting in asphyxiation. Carbon monoxide is formed whenever carbon or substances containing carbon are burned with an insufficient air supply. Even when the amount of air is theoretically sufficient, the reaction is not always complete, so that the combustion gases contain some free oxygen and some carbon monoxide.

An incomplete reaction is especially probable when it takes place quickly, as in an automobile engine; for this reason, automobile-exhaust gases contain harmful quantities of carbon monoxide, sometimes several percent, although antipollution devices are intended to keep the level below 1 percent. As little as 1/1000 of 1 percent of carbon monoxide in air may produce symptoms of poisoning and as little as a fraction of 1 percent may prove fatal in less than 30 min. Carbon monoxide is a major component of air pollution in urban areas. In addition to being present in automobile exhaust, carbon monoxide also occurs in cigarette smoke.

Because it is odorless, carbon monoxide is an insidious poison. It produces only mild symptoms of headache, nausea, or fatigue, followed by unconsciousness. An automobile engine running in a closed garage can make the air noxious within a few minutes; a leaking furnace flue may fill a house with unsuspected poison. Fuel gas, which may contain as much as 50 percent carbon monoxide, often has small quantities of unpleasant-smelling sulfur compounds purposely added to make leaks noticeable.

Carbon monoxide is an important industrial fuel because it contains more than two-thirds of the heating value of the carbon from which it was formed. It is a constituent of water gas, producer gas, blast furnace gas, and coal gas. In smelting iron ore carbon monoxide formed from coke used in the process acts as a reducing agent, that is, it removes oxygen from the ore. Carbon monoxide combines actively with chlorine to form carbonyl chloride, or phosgene, and it combines with hydrogen, when heated in the presence of a catalyst, to form methyl alcohol. The direct combination of carbon monoxide with certain metals, forming gaseous compounds, is used in refining those metals, particularly nickel.

About the Author

Dr.Badruddin Khan teaches Chemistry in the University of Kashmir, Srinagar, India.

(ArticlesBase SC #628347)

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The EPA Drafts Legislation To Track and Report Carbon (CO2) Emissions

By: Daniel Stouffer

Mandatory carbon (CO2) emissions reporting is more important than ever as the United States works with facilities to reduce substances known to adversely affect air quality, the climate, and lead to global warming. Most of the known matter that is destroying the earth's ozone layer and contributing to global warming is derived from manmade compounds and chemicals with high global warming potential (GWP) and commonly known as greenhouse gases (GHGs).

Around the country a comprehensive initiative, which includes mandatory carbon emissions reporting has been introduced by the Environmental Protection Agency (EPA) with the intention of controlling carbon dioxide (CO2) and greenhouse gases (GHGs) that have an effect on global climate change. Unfortunately, some substances like refrigerant gases not only have high global warming potential but they also destroy the ozone layer when emitted into the atmosphere.

The U.S. The Environmental Protection Agency (EPA), working in cooperation with many international governments, reiterate a common message related to the dangers of carbon emissions. CO2 and its unrestricted use will only lead to more environmental damage therefor more regulations will continue to limit carbon emissions in the future. A measuring, managing, and mitigating greenhouse gas emission places the foundation for future carbon emissions trading schemes within the United States. The European Union has worked on carbon emissions reductions as part of The Kyoto Protocol for a number of years. At a meeting planned in late 2009, global leaders in the fight against climate change will rework and redefine the next set of rules to follow The Kyoto Protocol. The U.S. under leadership form President Obama plan to be active participants.

As part of the draft greenhouse gas (GHG) regulations, any organization that uses refrigerant gases or other regulated substances would be required to comply with mandatory carbon emissions reporting. In addition to refrigerant gases, the following 6 chemical compounds all factor into a comprehensive carbon accounting. The Kyoto Protocol establishes legally binding commitments for the reduction of four greenhouse gases; carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), sulphur hexafluoride (SF6), and two groups of refrigerant gases; CFCs and PFCs.)

Refrigerant gases are known to affect the atmosphere and contribute to global warming. Numerous gases are listed in the EPA regulations including nitrous oxide, methane, carbon dioxide, hydrofluorocarbons, perfluorocarbons, nitrogen trifluoride, and ethers. Refrigerant gases, such as hydrofluorocarbons (CFCs), must be managed, tracked, and reported under the existing Montreal Protocol. There is some cross-over between the different regulations that restrict harmful emissions. The good news is any CO2 related tracking will further enhance emissions management practices already in place across an organization.

The EPA's mandatory carbon emissions reporting plan comes into effect in 2010. Companies must file a first report in 2011 covering the previous year. These requirements cover those facilities with HVAC systems, refrigeration and AC systems, companies that make industrial chemicals, as well as fossil fuels, engines and automobiles. Many industrial chemicals harm the environment by destroying the ozone layer or enhance global warming. The following chemicals, such as refrigerant gases, lead to harmful effects on the environment: chlorofluorocarbons, hydrofluorocarbons, halons, methyl chloroform, chlorine, fluorine, bromine and carbon tetrachloride amongst others.

The U.S. Clean Air Act, in addition to the mandatory emissions reporting by amounts, calls for the facilities and municipalities alike to monitor and track and subsequently report harmful substances, such as refrigerant gases that are in common use. Organizations that either cannot comply or choose to not follow the environmental regulations will be fined by the EPA. On top of regulatory fines, companies may experience a financial loss when they are required to buy carbon credits to meet the cap requirements.

Organizations can comply with CO2 emissions management regulations and reporting in a couple of ways. Monitoring and tracking can be handled manually and the reports completed by hand. However this approach can be very time-consuming and error-prone, and many will opt to use a software program or a web-based application to automatically handle the monitoring and tracking requirements of greenhouse gases (GHGs). Automation helps to ensure that reports are accurate and timely. Service automation or CMMS systems can lead the way to effective company operations. It is more efficient to maintain assets at optimal working conditions and collect relevant carbon related emissions data across distributed enterprises or systems.

Mandatory carbon emissions reporting will definitely lower this country's greenhouse gas emissions. The government has said that 13,000 facilities are responsible for between 85 and 90% of the harmful substances in the air.

The United States, through the implementation of a mandatory carbon emissions reporting program, ensure that businesses will reduce their carbon footprint and will help to mitigate adverse climate changes in the years ahead. This initiative is being repeated at various locations worldwide with the aim of addressing climate change head on - in as straightforward of a manner with immediate financial incentives to drive rapid and economy wide adoption of carbon reduction and market-based trading.

About the Author

To learn more effective refrigerant management tactics and the tools that support them, you can contact Daniel Stouffer, the Product Manager for Refrigerant Tracker. This web-based software makes it easy to monitor, manage, and report refrigerant gas usage. Stay in compliance with refrigerant management regulations. Visit Verisae's http://www.Refrigerant-Tracker.com

(ArticlesBase SC #836612)

Article Source: http://www.articlesbase.com/ - The EPA Drafts Legislation To Track and Report Carbon (CO2) Emissions

California Global Warming Solutions Act (ab 32): an Introduction to Refrigerant Gas Management

By: Daniel Stouffer

How to stay ahead and address the early action requirements for Stationary Equipment Refrigerant Management to be included in updates to AB 32.

The California Global Warming Solutions Act (AB 32), first passed in 2006 with additional early actions taking effect in 2010, is a broad and comprehensive directive with the goal of reducing greenhouse gasses (GHGs) by approximately 25% by the year 2020. This objective of the early action stems from increases in carbon equivalent emissions in California since 1990. The intent of the legislation to reduce greenhouse gasses to their 1990 levels, thereby reversing 16 years of pollution in less than 14 years.

As part of the California Global Warming Solutions Act (AB 32) the Air Resources Board (ARB) has approved an early action measure to reduce high-global warming potential (GWP) greenhouse gas (GHGs) emissions by establishing new legislation and defining requirements related to improved monitoring of AC/HVAC systems, enforcement of regulations, reporting of refrigerant usage, and recovery, recycling, or destruction of high-GWP refrigerant gases.

The greenhouse gasses (GHGs) as defined by the California's AB 32 are identical to those gasses identified in the Kyoto Protocol. These gases are already being regulated, monitored, and managed by many other countries around the World. In addition to carbon dioxide (CO2), which is the most widely known GHG, the following gasses are also defined as GHGs with high global warming potential (GWP) carbon equivalent emissions by the AB 32 legislation:

* Methane (CH4): a byproduct of waste decomposition, and natural geological phenomena; the majority of methane is derived from natural gas drilling.

* Nitrous Oxide (N2O): a pollutant created by industrial processes, motor vehicle exhaust, and industrial air pollutants reacting with the atmosphere; like methane, nitrous oxide can also be a product of waste decomposition in nature and agriculture.

* Sulfur Hexafluoride (SF6): a gas used for various electrical applications, including gas insulated switchgear. Sulfur Hexafluoride is also used for experimental applications.

* Perfluorocarbons (PFCs) and Hydrochlorofluorocarbons (HCFCs): a collection of commonly used refrigerant and aerosol gasses with a wide variety of other commercial applications. CFCs and HCFCs are considered Ozone Depleting Substances (ODSs), as defined in title VI of the US Clean Air Act (Section 608).

The California EPA's Air Resources Board (CARB) has developed a complex and highly detailed system of greenhouse gas management for refrigerant gasses, known as the Stationary Equipment Refrigerant Management Program, and stricter standards for new or existing refrigeration systems installation and ongoing maintenance. According to CARB this strategy includes careful monitoring of potential refrigerant gas leaks, improved record keeping and certification of personnel as well as specifications for PFC and HCFC recovery equipment.

The proposed Stationary Equipment Refrigerant Management Program, which integrates two AB 32 early action measures, addresses the detailed monitoring and management of the PFCs and HCFCs noted above and includes tracking requirements for new and existing commercial and industrial refrigeration systems. Likely to be implemented by January, 2010, is the monitoring and management of high global warming potential (GWP) refrigerants in large systems in the range of 2,000 pounds of refrigerant gas.

CARB is charged with the monitoring GHGs and high GWP gasses, as well and the eventual development and enforcement of specific and quantitative new regulations covering Refrigeration Video which refrigerant management with the tracking, reporting, cylinder management, and gas recovery for stationary refrigerant and air conditioning (AC) systems all becoming key integral parts.

The CARB proposal could also involve fines for mismanagement of refrigerant record keeping, intentional venting of systems, and the inability to regularly submit the required refrigerant usage reports. The California Air Resources Board (CARB) is an extension of the EPA and works to monitor and enforce the US Clean Air Act. Section 608 of the Air Act regulates refrigerant gas usage, leaks, recovery, and annual reporting.

The overall intent of CARB's strategy is to monitor and reduce the introduction of man-made GHGs and high GWP gasses into the atmosphere, as called for in the California Global Warming Solutions ACT (AB 32) in effect since 2006 with tighter controls, monitoring, and overall regulations becoming enforceable by early 2010.

Refrigerant gas monitoring, tracking, and management are important business planning considerations. Just like organizations manage assets, like a delivery truck, the consequences the release of high GWP gases, such as refrigerant gases, must be consider. Refrigerants cost money, harm the ozone and environment, and are subject to mandatory carbon emissions reporting. As organizations with AC/HVAC systems containing refrigerant gas of 50 pounds or more will soon find out, the effective monitoring, management of data, and systematic reporting of refrigerant usage will be key to business success in our emerging carbon economy.



About the Author

To learn more effective refrigerant management tactics and the tools that support them, you can contact Daniel Stouffer, the Product Manager for Refrigerant Tracker. This web-based software makes it easy to monitor, manage, and report refrigerant gas usage. Stay in compliance with refrigerant management regulations. Visit Verisae's http://www.Refrigerant-Tracker.com

(ArticlesBase SC #734799)

Article Source: http://www.articlesbase.com/ - California Global Warming Solutions Act (ab 32): an Introduction to Refrigerant Gas Management

Carbon Dioxide Could Replace Global-Warming Refrigerant

ScienceDaily (July 4, 2000) — WEST LAFAYETTE, Ind. – Researchers are making progress in perfecting automotive and portable air-conditioning systems that use environmentally friendly carbon dioxide as a refrigerant instead of conventional, synthetic global-warming and ozone-depleting chemicals.

It was the refrigerant of choice during the early 20th century but was later replaced with manmade chemicals. Now carbon dioxide may be on the verge of a comeback, thanks to technological advances that include the manufacture of extremely thin yet strong aluminum tubing.

Engineers will discuss their most recent findings from July 25 to 28, during the Gustav Lorentzen Conference on Natural Working Fluids, one of three international air-conditioning and refrigeration conferences to be held concurrently at Purdue University. Unlike the two other conferences, the biannual Gustav Lorentzen Conference, which is being held for the first time in the United States, focuses on natural refrigerants that are thought to be less harmful to the environment than synthetic chemical compounds.

"The Gustav Lorentzen Conference focuses on substances like carbon dioxide, ammonia, hydrocarbons, air and water, which are all naturally occurring in the biosphere," says James Braun, an associate professor of mechanical engineering at Purdue who heads the organizing committee for all three conferences. "Most of the existing refrigerants are manmade."

Purdue engineers will present several papers detailing new findings about carbon dioxide as a refrigerant, including:

• Creation of the first computer model that accurately simulates the performance of carbon-dioxide-based air conditioners. The model could be used by engineers to design air conditioners that use carbon dioxide as a refrigerant. A paper about the model will be presented on July 26 during a special session sponsored by the U.S. Army in which researchers from several universities will present new findings.

• The design of a portable carbon-dioxide-based air conditioner that works as well as conventional military "environmental control units." Thousands of the units, which now use environmentally harmful refrigerants, are currently in operation. The carbon dioxide unit was designed using the new computer model. A prototype has been built by Purdue engineers and is being tested.

• The development of a mathematical "correlation," a tool that will enable engineers to design heat exchangers – the radiator-like devices that release heat to the environment after it has been absorbed during cooling – for future carbon dioxide-based systems. The mathematical correlation developed at Purdue, which will be published in a popular engineering handbook, enables engineers to determine how large a heat exchanger needs to be to provide cooling for a given area.

• The development of a new method enabling engineers to predict the effects of lubricating oils on the changing pressure inside carbon dioxide-based air conditioners. Understanding the drop in pressure caused by the oil, which mixes with the refrigerant and lubricates the compressor, is vital to predicting how well an air conditioner will perform.

Although carbon dioxide is a global-warming gas, conventional refrigerants called hydrofluorocarbons cause about 1,400 times more global warming than the same quantity of carbon dioxide. Meanwhile, the tiny quantities of carbon dioxide that would be released from air conditioners would be insignificant, compared to the huge amounts produced from burning fossil fuels for energy and transportation, says Eckhard Groll, an associate professor of mechanical engineering at Purdue.

Carbon dioxide is promising for systems that must be small and light-weight, such as automotive or portable air conditioners. Various factors, including the high operating pressure required for carbon-dioxide systems, enable the refrigerant to flow through small-diameter tubing, which allows engineers to design more compact air conditioners.

More stringent environmental regulations now require that refrigerants removed during the maintenance and repair of air conditioners be captured with special equipment, instead of being released into the atmosphere as they have been in the past. The new "recovery" equipment is expensive and will require more training to operate, important considerations for the U.S. Army and Air Force, which together use about 40,000 portable field air conditioners. The units, which could be likened to large residential window-unit air conditioners, are hauled into the field for a variety of purposes, such as cooling troops and electronic equipment.

Freon

"Freon" is a trade name for a family of haloalkane refrigerants manufactured by DuPont and other companies. These refrigerants were commonly used due to their superior stability and safety properties: they were not flammable nor obviously toxic as were the fluids they replaced, such as sulfur dioxide. Unfortunately, these chlorine-bearing refrigerants reach the upper atmosphere when they escape. In the stratosphere, CFCs break up due to UV-radiation, releasing their chlorine atoms. These chlorine atoms act as catalysts in the breakdown of ozone, which does severe damage to the ozone layer that shields the Earth's surface from the Sun's strong UV radiation. The chlorine will remain active as a catalyst until and unless it binds with another particle, forming a stable molecule. CFC refrigerants in common but receding usage include R-11 and R-12. Newer refrigerants that have reduced ozone depletion effect include HCFCs (R-22, used in most homes today) and HFCs (R-134a, used in most cars) have replaced most CFC use. HCFCs in turn are being phased out under the Montreal Protocol and replaced by hydrofluorocarbons (HFCs), such as R-410A, which lack chlorine. However, CFCs, HCFCs, and HFCs all have large global warming potential.

Newer refrigerants are currently the subject of research, such as supercritical carbon dioxide, known as R-744.[4] These have similar efficiencies compared to existing CFC and HFC based compounds, and have many orders of magnitude lower global warming potential.

The thermodynamics of the vapor compression cycle can be analyzed on a temperature versus entropy diagram as depicted in Figure 2. At point 1 in the diagram, the circulating refrigerant enters the compressor as a saturated vapor. From point 1 to point 2, the vapor is isentropically compressed (i.e., compressed at constant entropy) and exits the compressor as a superheated vapor.

From point 2 to point 3, the superheated vapor travels through part of the condenser which removes the superheat by cooling the vapor. Between point 3 and point 4, the vapor travels through the remainder of the condenser and is condensed into a saturated liquid. The condensation process occurs at essentially constant pressure.

Between points 4 and 5, the saturated liquid refrigerant passes through the expansion valve and undergoes an abrupt decrease of pressure. That process results in the adiabatic flash evaporation and auto-refrigeration of a portion of the liquid (typically, less than half of the liquid flashes). The adiabatic flash evaporation process is isenthalpic (i.e., occurs at constant enthalpy).

Between points 5 and 1, the cold and partially vaporized refrigerant travels through the coil or tubes in the evaporator where it is totally vaporized by the warm air (from the space being refrigerated) that a fan circulates across the coil or tubes in the evaporator. The evaporator operates at essentially constant pressure. The resulting saturated refrigerant vapor returns to the compressor inlet at point 1 to complete the thermodynamic cycle.

It should be noted that the above discussion is based on the ideal vapor-compression refrigeration cycle which does not take into account real world items like frictional pressure drop in the system, slight internal irreversibility during the compression of the refrigerant vapor, or non-ideal gas behavior (if any).

Refrigerants in subcritical applications

In subcritical applications, refrigerant is metered by a capillary tube or thermostatic expansion valve, the control strategy being to inject liquid into the evaporator and maintain a given superheat entering the compressor. The metering device is selected or designed to ensure that there is complete evaporation ahead of the compressor.

Superheat is maintained to ensure that evaporator efficiency is optimal, and that liquid refrigerant does not enter the compressor. Excessive superheat may lead to overheating of the compressor.

In systems where a thermostatic expansion valve is used rather than a capillary tube, superheat is maintained by placement of a sensing bulb at the outlet of the evaporator. The modulation of the valve is then controlled by the temperature transmitted to it from the bulb and the pressure at an internal or external equalization port.

A different control strategy is needed in transcritical cycles.

A system based on the transcritical CO2 cycle uses a high pressure expansion valve (HPEV). Rather than controlling refrigerant metering from the low-pressure side of the system, modulation control comes from the high side of the system. A mechanical HPEV will control refrigerant injection into the evaporator by opening and closing based on the increase or decrease in gas cooler pressure.

In the HPEV, spring force is a closing force that acts on the top of a diaphragm. Increasing spring force throttles the valve, causing a backpressure in the gas cooler; the valve will not open until that back pressure, opposing spring force, increases to the point where it can overcome spring force and open the valve. The valve set point for the inlet pressure can be adjusted manually by compressing a spring in the valve.

Unlike a TEV, an HPEV does not control evaporator superheat. The HPEV injects refrigerant into the evaporator, but superheat is not directly controlled — instead it is indirectly regulated by system design.

The system charge, its distribution between the components, evaporator design, and the heat load, along with other external operating conditions, determines system superheat. By controlling the gas cooler pressure, the HPEV will indirectly influence system superheat, but the system must be designed so that liquid refrigerant in the evaporator outlet is not allowed to return to the compressor.

The HPEV was designed to control gas cooler pressure rather than suction line superheat as does a TEV. An HPEV, therefore, must withstand high-side CO2 pressures that can reach 1500 psia, at the same time accurately controlling gas cooler pressure. Slight capacity and energy efficiency (COP).

Varieties of Natural Refrigerants

Ammonia is a very good refrigerant and is used to a significant extent in large warehouses. Ammonia is toxic and, under certain limited conditions, flammable and even explosive. However, with its intense, pungent odor, it is a self-alarming refrigerant. Ammonia has emerged as a refrigerant for water chillers in Europe. These units are entirely self-contained, including a gastight cabinet that houses the entire unit and a water tank to dissolve any ammonia in case of a leak. These measures, to be sure, increase costs considerably.

Hydrocarbons are excellent refrigerants, but they are also flammable and explosive. In North America, any flammability risk is unacceptable, but some countries in Europe and elsewhere have less-stringent liability laws. Since the mid-1990s, virtually all refrigerator production in Germany has used hydrocarbons as the working fluid. Some heat pump manufacturers whose systems are installed entirely outdoors have followed suit, and some commercial installations have recently become publicly known. Nevertheless, the danger of fire remains an overriding concern. To address this challenge with safety features, the cost of a system would have to be increased by about one-third.

Carbon dioxide is a refrigerant that operates at very high pressures in a transcritical cycle for most operating conditions. Thus the refrigerant condenser of a conventional refrigeration system serves now as a cooler for supercritical fluid. Only after the expansion process is liquid carbon dioxide available to provide cooling capacity through evaporation. Because of the nature of the transcritical cycle, the efficiency of carbon dioxide is quite poor. However, this is its only disadvantage. All the other characteristics of carbon dioxide are very favorable. It is environmentally safe, has very low toxicity, and allows for extremely compact systems. The vapor pressure of CO2 is approximately seven times higher than that of R-22. Moreover, the supercritical CO2 has a higher density than subcritical fluids, so there is potential to reduce the size of hardware. There are indications that with modern materials and technologies, the weight of CO2 heat exchangers can be reduced considerably, especially for tap water heating, with essentially the same performance.

Natural Refrigerants & Carbon Dioxide

Substances such as air, water, ammonia, hydrocarbons, and carbon dioxide may provide solutions to the problem of finding environmentally acceptable refrigerants.

By Yunho Hwang, Michael Ohadi, and Reinhard Radermacher
Refrigeration and air conditioning play important roles in modern life. They not only provide comfortable and healthy living environments, but have also come to be regarded as necessities for surviving severe weather and preserving food. Unfortunately, accelerated technical development and economic growth in much of the world during the last century have produced severe environmental problems, forcing us to acknowledge that though these technological advances may contribute to human comfort, they also can threaten the environment through ozone depletion and global warming. Aside from cost reduction, these concerns are the biggest driving forces for technical innovation in the field of refrigeration and air conditioning.

Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs)—used as working refrigerants in refrigerators and air conditioners as well as blowing agents in foams—are now being regulated because of their contribution to ozone depletion. Hydrofluorocarbons (HFCs) could be useful as short- and midterm replacements, but may ultimately not be suitable, owing to their high global-warming potential (GWP). Accordingly, a long-term solution will require the use of natural refrigerants. The refrigerator and automotive air-conditioning industries have already begun to address the challenges of replacing HCFCs, including R-22, and, eventually, HFCs on a global level.

The second, more important reason, dealt with thermodynamics. Gerrard says that to reach the operating temperature that they require (–18 DegF) using a CO2 system would have meant using two compressors in order to reach the same energy efficiency as the hydrocarbons.

When choosing propane, they were initially concerned about safety issues. “The first question we had was the flammability of the refrigerant,” he says. “But, we knew that isobutane and propane have approximately the same flammability rating and that in the year 2000, there were about 120 million domestic refrigerators and freezers using isobutane and we weren’t aware of any accidents.”

Unilever undertook a number of risk assessments before the introduction of the hydrocarbon cabinets. The company also did leak testing and found that the leak rates for hydrocarbons in operation were “very, very low,” he says, in line with HFC refrigerated cabinets.. Leak rates are in the range of grams per year, he says, and at this rate it was highly unlikely that flammable mixtures could be formed.

In the US new rules come into effect on Jan. 1, 2010, restricting the use of hydrochlorofluorocarbons in refrigerants for air-conditioning systems, geothermal heat pumps and the chillers used to cool large residential and office buildings.





Co2 as a Refrigerant

Even though Hydrofluoro compounds (HFC) are widely used as refrigerants because of their environment friendly nature (no damage to ozone layer), CO2 is also a popular choice as refrigerant.

Some of the advantages of CO2 as a refrigerant are:

• widely available;
• high volumetric cooling capacity and heat transfer;
• no recovery or recycling required;
• non inflammable and non toxic;
• environment friendly;
• the compressors are compact in size

Some of the difficulties is using CO2 as refrigerant are: high working pressure and large pressure difference (3 to 5 times conventional refrigerants); low theoretical efficiency with normal refrigeration systems. Hence it requiresadvanced technology compressor and refrigeration system. The hoses need to be strong as well as the evaporators and gas coolers are used instead of condensers as there is no phase change of the refrigerant. They are widely used in vending machines.

One of the difficulties of CO2 as a refrigerant is its detection and level control.

Chemical sensor elements cannot reliably measure CO2 levels. Other alternate detectors include infrared sensors.

China Refrigeration: Walking on the CO2 path - Part I

The world’s third largest trade show for heating and cooling was, as expected, dominated by solutions for conventional refrigerants. However, a surprising number of global players presented CO2 components set to be sold on the Chinese market in a few years time. In a technical seminar, Bitzer updated Chinese experts on latest developments regarding CO2 compressors.

At the China Refrigeration, held last week from 5-7 April in Guangzou, companies known to be involved in CO2, nearly animously agreed that the natural refrigerant would certainly be a solution to be taken to the Chinese market in the near future. At present however, and also looking at cost cutting tendencies in the industry, CO2 would remain mainly in the testing phase, with commercialisation to be expected over the next few years.

Technical Seminar on CO2 compressors

In its technical presentation to around 100 industry experts and engineers, German compressor manufacturer Bitzer updated on the performance and operation of its CO2 range. In a packed room, Bitzer representatives from China started off by explaining basic characteristics of R744, its behaviour compared to R22 or R404a, differences between transcritical and subcritical operation, and the compact design of CO2 compressors. The compressor maker then went on to elaborate on the different system layouts used with R744, specific design options, and efficiency comparisons between the natural and chemical refrigerants.

Participants were highly interested in technical details regarding high-pressure R744 systems. Lively discussions centred around the questions of oil return, the materials used for CO2 compressors, the preferred hybrid systems used in European supermarkets, and better cooling systems in a Chinese test system using R404a-R744.

Liquid CO2 - an alternative to freon for the frozen food shipping industry

Frozen Food Digest, Oct, 1992 Frozen Food Digest, Oct, 1992

Cryocon Containers Inc., a publicly owned Vancouver, Canada based Company and their joint venture partner Pacific Shipping Systems Inc., have introduced the first 48 foot Domestic Intermodal container to the U.S. frozen food industry using liquid CO2 as the refrigerant, replacing current mechanical CFC based freon coolants.

Continued testing of the finished model using state of the art container technology has reaffirmed the superiority (proven earlier in railcars) of the system over conventional mechanical reefers. One recent test, initiated jointly with Burlington Northern Railway and their customer Twin City Foods, a leading National Distributor, entailed transporting a load of frozen corn at zero degrees F. from Ellensburg, Washington to Lake Odessa, Michigan. The trip was five and a half days with the load arriving at zero degrees F. Tom Matheson, Traffic and Distribution Manager at Twin City Foods was quoted as saying "everything went perfect" and "we feel that the cryogenic container will fit into the frozen market quite well."

The system, which has no mechanical moving parts, is cost competitive to build, economical to operate, allows competitive cubic space for product and has no maintenance requirements necessary to conventional mechanical reefers. The advantages bring overall shipping costs down dramatically.

The CO2 cryogenic technology was first introduced in the early 1980's when Van Thomsen, then of Liquid Air Corporation, together with the American Frozen Food Institute and Burlington Northern Railway built a working prototype railcar with a system whereby liquid CO2 is pumped into a bunker located in the top of the car where it turns into dry ice snow. Through the natural process of warm air rising inside the product storage area, the dry ice snow sublimates and cryogenic gas drops down and maintains the temperature of the frozen product.

Cryocon Containers Inc., using the latest Thomsen technology, is now able, for the first time, to install their system into thin skinned Intermodal and I.S.O. containers as well as over-the-road truck trailers.

The supply of commercial liquid CO2 is readily available, inexpensive and also causes no net effect on the ozone layer.

Cryocon is currently building an over-the-road trailer for an International food distributor, five 40 foot I.S.O. ocean containers and five 48 foot Intermodal containers for marketing purposes to frozen food processors, third party shippers and premier shipping lines. The company uses established quality manufacturers under license to build the containers incorporating the technology from the ground up.

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