Ammonia refrigeration system basics of investing
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Ammonia refrigeration system basics of investing inside track betting san andreas map images
Industrial Refrigeration system Basics - Ammonia refrigeration working principleDIMSUM BREAK BTC DELIVERY
Since ammonia is plentiful, the cost is low. There are two primary grades of ammonia commonly available in the marketplace. There is an agricultural or commercial-grade ammonia that must contain a minimum water content of at least 2, ppm water 0. The minimum water content prevents stress corrosion cracking of the metals used in equipment for the agricultural industry.
Industrial-grade anhydrous ammonia, commonly called metallurgical or refrigeration grade, has very little water contamination. Metallurgical-grade has a maximum of about 33 ppm water 0. For optimum efficiency and effectiveness in your refrigeration system, the ammonia supplied to you for your system should meet or exceed these specifications. In addition to the price the most compelling reason to utilize anhydrous ammonia is the fact that it has such a high latent capability per pound.
When compared with R, which is approximately 69 Btu per pound at the same temperature, its obvious that it takes less ammonia to do the work because it is more efficient. This means less kwh used and lower operating costs. Typical Systems The best way to understand ammonia refrigeration sytlems is to review the basic designs used today.
Some ammonia-based systems are similar to designs used in hvacr systems that use halocarbons. The differences are somewhat obvious but offer just enough differences to challenge technicians from either field. We will discuss the benefits, drawbacks and special problems associated with each type of system. Three basic types of systems exist: thermal expansion valve TXV , flooded and liquid recirculating or liquid overfeed. Thermal Expansion Valve TXV Systems These are also referred to as dry systems, meaning that the existing refrigerant is free from liquid.
These systems are not the most efficient, as it is necessary to ensure that all refrigerant is boiled off prior to the vapor entering the compressor. This necessitates larger evaporator coils. To ensure complete vaporization, a thermal expansion valve is used to control flow see Figure 1. Although they are less efficient, the TXV systems are simpler in design, require less refrigerant charge, cost less initially and usually have less oil-logging problems. Figure 1.
Depending on the temperature, the boiling vapor can increase in volume between to times and unless the coils are large in diameter, slugs of liquid will be carried out with the vapor. As the liquid boils, fluctuation, which is similar to the boiling process in a boiler, occurs within the evaporator.
Many thermal expansion systems are in use today. They work well as long as there are minor load swings in the system. This is due to the use of more wetted evaporator surface. The flooded system uses about 25 percent less surface than a TXV system to remove the same amount of heat, therefore, the coil cost is less.
However, the cost of the control system usually is higher. A typical flooded system consists of a surge drum with some type of liquid-level control device, generally a low-side float see Figure 2. A liquid leg feeds the liquid to the bottom of the coils. As the liquid entrained with the gas is returned to the top of the surge drum, it falls into the leg and allows the gas to be drawn off the top into the suction of the compressor.
The system is designed to cause a boiling action that will result in about 2 to 3 pounds of liquid being recirculated for every pound of refrigerant evaporated. There is more refrigerant recirculated than vaporized. Some advantages of a flooded system compared to a TXV system include: More effective use of evaporator surfaces. Easier distribution of refrigerant with parallel systems.
Cooler vapor entering the compressor which reduces the discharge temperature. Some disadvantages include: More refrigerant is required in the system. Oil accumulation logging is more severe requiring closer monitoring. Figure 2. The flooded system uses about 25 percent less surface than a TXV system to remove the same amount of heat, so the coil cost is less.
In this system the amount of liquid refrigerant circulated through the evaporator is considerably in excess of that which can be vaporized. The recirculation ratio can be as high as This wetted vapor is returned to a low-pressure receiver where separation of the liquid and gas occurs see Figure 3.
The overfeed system ensures that a constant liquid level is maintained in the accumulator sometimes referred to as a low-pressure receiver. Figure 3. The liquid pump recirculation system ensures the constant liquid level is maintained in the accumulator, sometimes referred to as a low pressure receiver. The advantages in a liquid overfeed system include: High system efficiency. Efficient hot gas defrosting capability. Simplified oil draining and return. Lower coil temperatures.
Larger refrigerant charge is required. Larger piping is required. The Safety Factor How dangerous is ammonia? No more so than any other Class II refrigerant, meaning it should be treated with respect. However, ammonia systems generally are safe. The U. One advantage of ammonia over halocarbon-based refrigerants is that it is self-alarming due to its strong and distinct odor.
The following table lists some of the possible effects of ammonia in the air: Because the smell of ammonia is readily perceptible, you will know it if there's even a tiny leak. Ammonia vapor is lighter than air and in a confined area il displaces oxygen from the ceiling downward. Halocarbons are heavier than air and will displace the oxygen from the floor upward. Either situation can be fatal.
Ammonia is flammable and has a lower explosive limit LEL of 15 percent , ppm and an upper explosive limit UEL of 28 percent , ppm. When the ammonia vapor is mixed with a mistable oil, the LEL can be as low as 8 percent 80, ppm. This means it will break down into nitrogen and hydrogen gases. Hydrogen gas has a flammability range of 4 to 75 percent.
Ammonia systems generally are built around an understanding of the characteristics of anhydrous ammonia and its dangers and benefits. As with any system, the first line of defense is the safety engineering designed into it. Industry safety standards continue to be the main reason ammonia systems are much safer than most people are aware. Each system must meet strict safety codes, which include materials of construction as well as appropriate relief valves, ventilation, safety switches and other safety engineering concerns.
Training And Safety As in any other industry, the training of operators and technicians is important. Fully trained operators and technicians are much less likely to cause a situation resulting in death or injury. EPA address training for larger ammonia refrigeration systems.
If the ammonia refrigeration system has a charge of 10, pounds or more, you must implement or take operational and maintenance training. Many companies follow this regardless of the charge level. Training must include standard operating procedures for every task that will be performed, as well as safe work practices, including proper line-break procedures.
Line-break procedures are what a technician does each time the ammonia refrigeration system is opened for maintenance. Additionally, operating personnel must receive refresher training at least every three years. Finding Ammonia System Leaks The second part of a series on ammonia refrigeration systems explores the various tools and sensors that are available to help service techs find system leaks Part one on ammonia refrigeration systems in last month's issue of RSES Journal explored the basics of ammonia refrigeration and the types of systems generally found in the industry This article will cover the tools and sensors that are available to help service techs and system operators locate leaks.
Most modern ammonia systems are computer controlled in one manner or another. They require an initial setup which consists of the basic programming of the operating system. This is when a system's operational parameters and set-points are established. A system's performance is dictated by the set-points burned into the software that controls the normal operation of the compressors, condensers, fans, evaporators and other essential components.
Many older systems are either manually operated or partially computerized, which creates a different set of operational tasks. As with any refrigeration system, safety devices and controls are essential to assure safe operation under normal and abnormal conditions. Many different devices are used to perform different tasks during the course of a normal operating day. Float switches have been used in our industry for many years, and although they have become more sophisticated they still perform the same basic functions.
Many are used to control refrigerant levels as well as control on and off functions of solenoid valves and regulators. Several other devices function as safety switches, valves, pressure regulators and electrical interlock devices. The number of devices is so large that it is beyond the scope of this article to detail all of them. Finding Leaks Refrigerant leaks can be a problem in any refrigeration system.
Mechanical seals as well as valve packings can fail and allow ammonia to vent into the atmosphere. Anhydrous ammonia, which is a formulation void of water, is self-alarming due to its strong odor. However, leaks sometimes can be seen as well as smelled. In other situations, leaks are less noticeable and can be difficult to find in a large refrigeration system, Anhydrous ammonia is a Class I refrigerant and is an inhalation irritant as well as a caustic.
This can create a problem for most of us because humans cannot tolerate exposure to large amounts of this refrigerant very well. Levels of concentration and resulting protective actions taken will varv. At a low concentration level of 0 to 25 parts per million ppm , no respirator is required and a person can work for eight hours without any adverse effects.
At a concentration level of ppm a full-face air purifying respirator must be worn. Above ppm a self-contained breathing apparatus SCBA must be worn. Additionally, a fully encapsulated suit must be worn when the concentration level is injurious to the skin. This level begins at around to ppm. It is common to put on the suit when the SCBA is worn. A full face respirator must be worn when ammonia concentrations in the air reach ppm. To safely operate a refrigerant system, you must use sensing devices that alert building operators and occupants of a refrigerant leak.
These devices are available in a wide range of sophistication and features. They can have integrated horns or lights or can send a signal to a monitoring service. Calibrate these devices on a regular basis, The most popular of them utilizes an electrochemical sensor. The sensor contains a cell whose life is dependent upon the amount of ammonia it is exposed to as well as air temperatures it is subjected to, and must be replaced every two years, These sensors also must be replaced when they can no longer be calibrated.
Automated functions of these devices include turning on exhaust fans, turning off liquid feed solenoids or even shutting down the entire refrigeration system. An alarm system is just one of many tools that will ensure that the system is operating as safely as possible. Top-mounted lights visually indicate that a certain level of contamination has been reached or that an alarm has been activated. These units are either mounted in each room that contains ammonia equipment or centrally located utilizing remote sensors to trigger the signaling device.
The unit, which is permanently mounted on a wall, allows the operator to adjust the concentration range ppm to reach before sending a signal. This is useful as the placement of the unit may require a less sensitive response due to possible higher concentration levels during maintenance tasks. This fixed-type of sensor has been used for many years and comes in many different designs. Meeting the need for smaller, more portable units has proven a challenge as the level of detection and the durability factors come into play.
Above are a few of the portable sensing devices used for sampling the air for ammonia to help find leaks or to determine how much ammonia is present. Popular handheld units can work well to detect levels up to ppm and are easy to operate. For smaller leaks, the unit shown at the top right of this page works well.
Portable hand-held sensing units like this one work well on smaller ammonia leaks below ppm. Alarm systems can produce both visual and audible warning signals to alert those in the area that dangerous levels of ammonia concentration have been reached. Another type of unit shown above uses glass tubes that are sensitive to ammonia and graduated to reflect the current concentration ppm. A glass tube is inserted in the end of this unit after both tips have been broken off. The unit pictured is a draw-type bellows sampler, which draws a measured amount of air into the bellows through the glass tube.
Other samplers work in a similar fashion. The new and improved IIAR 2 is the definitive design safety standard of the ammonia refrigeration industry. Specifies criteria for materials, design parameters, marking and testing of valves and strainers used in closed circuit ammonia refrigeration systems. Written to serve as a standard for the installation of closed-circuit ammonia mechanical refrigeration systems and overpressure protection relief piping systems.
Provides basic minimum requirements for the safe start-up and commissioning of complete closed-circuit mechanical refrigerating systems utilizing ammonia as the refrigerant and additions and modifications made to such systems. Defines the minimum requirements for developing operating procedures that are easy to understand, safe, effective, reliable, and meeting applicable regulatory environments.
Specifies minimum criteria for removing the ammonia charge in conjunction with decommissioning of closed-circuit ammonia refrigeration systems. Standard 15 establishes procedures for design, construction, installation, inspection, testing, and operation of the equipment and systems using refrigerants. Standard 34 describes a shorthand way of naming refrigerants and assigns safety classifications based on toxicity and flammability data.
Provides recommendations and requirements for the safe and efficient design, construction, installation, operation, inspection, and maintenance of mechanical refrigerating and air-conditioning equipment aboard ships. Guidance with focus on preservation of the economic benefits of ammonia refrigeration while providing for the management of risks.
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