1. What Is Ammonia (r717 / Nh3)?
Ammonia is a common, naturally occurring compound in the environment. It can be naturally broken down into one atom of nitrogen and three atoms of hydrogen, its chemical formula therefore being NH3. Ammonia is a key intermediary in the nitrogen cycle for plants and animals, given that the atmosphere consists of nearly 80% nitrogen. It is essential for many biological processes.
In fact, ammonia is among the most abundant gasses in the environment. Used as a refrigerant, the colorless gas carries the designation R717 / R-717. Given its abundance in nature, ammonia is referred to as a “natural refrigerant”.
2. What Are The Main Advantages Of Ammonia As A Refrigerant?
Ammonia is one of the most climate-friendly and cost-efficient refrigerants to heat cool and freeze. It is also:
Non-ozone depleting: Ozone Depletion Potential = 0
Non-climate damaging: Global Warming Potential = 0
Abundant: part of natural cycles, essential for many biological processes
Safe: with proper handling
Energy-efficient: usually better energy efficiency than systems using chemical gases
Cost-efficient: low refrigerant purchase price, low system running costs
Readily available: worldwide
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3. How Is Ammonia Used As A Refrigerant?
Traditionally, refrigerant-grade ammonia has been used as a 99.98% pure substance, free of water and other impurities. It is readily available, inexpensive, and capable of absorbing large amounts of heat when it evaporates. Lately, new blends incorporating ammonia have been shown to provide additional benefits in terms of lower discharge outlet temperature, a lower compression ratio, and a higher refrigeration capacity. Blends include the hydrocarbons propane (R290), octafluoropropane (R218), octafluorocyclobutane (RC318), or isobutane (R600a). The blend R723 – consisting of 60% ammonia and 40% dimethyl ether – promises further potential in high temperature heat pumps.
4. Is Ammonia Safe?
Yes, with proper handling. In any mechanical refrigeration system, leaks will occur. This fact is exacerbated when the leaks involve odorless refrigerants hazardous to human health, or otherwise harmful for the environment.
Having been used as a refrigerant for more than 150 years, ammonia has a long safety record. The inherent safety of ammonia comes from its characteristic odour, which signals even the smallest leak, at concentrations far lower than any dangerous level. Moreover, its density and very limited range of flammability, advances in safety mechanisms and system designs (plate heat exchangers, separate sealed compartments, leak detection systems, electrical switching outside the compartments etc.), well-trained individuals working with R717 systems, as well as industry codes and standards have made sure that ammonia poses hardly any risk to human health.
As an example, the United States Chemical Safety Board (CSB) reports that R717 incidents led to only four fatalities in the ten-year period from 1994 to 2004. This compares with over 800 deaths from lightning strikes in the USA during the same period.
5. Is Ammonia Flammable?
Ammonia is difficult to ignite and exhibits a narrow range of flammability. It is flammable only at high concentrations and under extremely limited conditions. Because ammonia will not sustain a flame on its own, ignition of ammonia vapour requires an uninterrupted external flame source. Ammonia burning velocity, at a maximum of 8 cm/s, is substantially lower than other flammable refrigerants, and is not high enough to create an explosion. Properly designed ammonia refrigeration systems that are well ventilated and free of open flames or ignition sources are safe against potential explosion.
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6. Is Ammonia Toxic?
Yes. Ammonia carries a B2 safety classification, meaning that it can be toxic for humans at high concentrations. However, as even the slightest traces of ammonia can be detected in the air, a safe and immediate repair of a system leak is possible. Moreover, the easily detectable and penetrating odour will encourage individuals to leave the immediate area of release before any harmful concentration will occur. The safety record of ammonia refrigeration is also due to the fact that ammonia is 1.7 times lighter than air and thus easily vented by mechanical means into the atmosphere. If a leak occurs in a refrigeration system under pressure, only the pressurized gas and, absent additional heat, a smaller amount of the liquid in that space will be released.
The facts: The human body can handle ammonia in small quantities. Any amount in the atmosphere below 20 parts per million (ppm) is regarded as not dangerous. Already at amounts of up to 53 ppm, ammonia’s characteristic odour will be noticeable. At amounts of 300-400ppm, prolonged exposure will become unpleasant, and only in amounts over 700ppm it can start affecting human health. As a result, the incidence of fatality and serious injury in R717 systems is extremely low.
7. Does Ammonia Have An Impact On The Ozone Layer?
No. With an ozone depletion potential of 0, ammonia does not harm the atmospheric ozone layer in any sense.
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8. Does Ammonia Contribute To Global Warming?
No. Ammonia has a Global Warming Potential (GWP) of 0, meaning it doesn’t add to the greenhouse effect linked to global warming. In fact, ammonia, one of the most common compounds found in nature, is essential to the earth’s nitrogen cycle and its release in the atmosphere is immediately recycled. The use of ammonia as a refrigerant is therefore consistent with international agreements on reducing global warming and ozone depletion.
9. How Does An R717 System Reduce Greenhouse Gas Emissions?
To assess the complete environmental performance of refrigerants and their systems, both Direct and Indirect Emissions have to be considered:
Firstly, using ammonia reduces the direct greenhouse gas (GHG) emissions. This is due to its Global Warming Potential (GWP) of 0, compared to a GWP of 1,700 for R22 and 3,260 for R404a, and even higher values for other chemical refrigerants. Why is this important? As an example, from a typical industrial refrigeration system 10-25% of the total refrigerant charge is emitted to the atmosphere every year. Assuming that leakage rates are the same, ammonia will thus spare the planet tones of greenhouse gases compared to any other chemical refrigerant currently used. In addition, leakage rates for ammonia are considerably lower than for any other refrigerant as the gas is detected much earlier due to its characteristic odour.
Secondly, ammonia also leads to lower Indirect GHG emissions by maximizing energy efficiency of equipments in which they are used. This is due to a combination of factors, including its favorable thermodynamic characteristics. As a result, ammonia systems use less primary energy to produce a certain refrigeration effect compared to other commonly used refrigerants. Its indirect global warming effect is therefore one of the lowest of all refrigerants.
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10. Where Does The Ammonia Used As A Refrigerant Come From?
Presently, there are an estimated two billion metric tons of ammonia present in the world. Of this amount, approximately five percent is man-made. Approximately 18 million metric tons of ammonia are produced annually in North America alone, and of this amount, less than two percent is used for refrigeration.
11. Is Ammonia A Totally New Refrigerant?
No. Ammonia was first used as a refrigerant in the 1850s in France and was applied in the United States in the 1860s for artificial ice production. The first patents for ammonia refrigeration machines were filed in the 1870s. From all the refrigerants used in food processing, ice rinks, chillers and other applications, only ammonia has secured a lasting role as a refrigerant.
Even when halocarbons became the refrigerants of choice, ammonia remained the most used refrigerant for industrial applications in many countries. Because of ammonia’s proven applicability as a safe and efficient refrigerant for over 150 years, it is immediately available for wider usage and new applications. Today, ammonia remains the most commonly used refrigerant in large systems to process and preserve food and beverages.
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12. How Energy-efficient Is Ammonia?
Ammonia is capable of absorbing large amounts of heat when it evaporates. For industrial refrigeration, ammonia is generally accepted as the most efficient and cost effective refrigerant available. This, in turn, brings important benefits to consumers, as the lower operating costs contribute to lower food prices.
For chillers, ammonia can also offer optimal performance. As an example, the central ammonia chilling plant of London Heathrow’s new Terminal 5 uses four chillers, each with a cooling capacity of 6.6 mW, or 1,875 tones. The large-scale R717 chillers reduce energy consumption by at least 30% compared to smaller local chillers. Moreover, storing the chilled water reduces the system capacity and takes advantage of night electricity rates.
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13. In Which Applications Is Ammonia Used?
Ammonia is suitable for the following applications:
Food processing, Cold storage & Delivery: Ammonia refrigeration is the backbone of the food industry for freezing and storage of both frozen and unfrozen foods in many parts of the world (including fruits, vegetables, meat, poultry, fish, dairy, ice cream, beverages). In the range 50 kW to 200 kW ammonia may be used, and for larger freezers ammonia is almost always preferred due to improved energy efficiency and reduced leakage.
Petrochemical & Pharmaceutical industry, Mining: For many years, ammonia has been the refrigerant of choice in large industrial refrigeration applications, including process cooling, cold storage, the production of ice for use in chemical reactions, and mining. Ice plants are typically far larger than those found in the food industry.
Air Conditioning: Ammonia is increasingly used for air conditioning in public buildings, hospitals, colleges and office parks, as well as to enhance the efficiency of power generation facilities. Ammonia refrigeration has also been used to provide air conditioning for the International Space Station and the theme park Biosphere II, in the USA.
Chillers: Chillers using R717 and a secondary heat transfer fluid (intrinsic to chillers) are available in the capacity range from 200 to 2000 kW with a few larger models. They allow for the safe use of ammonia in large buildings. Ammonia can be used in absorption chillers – with water as the absorbent –, in screw chillers, or in reciprocating chillers. The new Terminal 5 of Heathrow, one of the world’s largest airports, is using a central ammonia chilling plant to provide all heating and cooling.
Supermarkets: More recently, ammonia has been used in conjunction with a secondary refrigerant such as carbon dioxide in a ‘cascade’ system, meaning that less ammonia is required to achieve satisfactory results, and that the ammonia charge can be contained in a plant room or other safe environment.
Marine refrigeration / Fishing vessels: R717 has been increasingly used in marine refrigeration equipment. Applications include its use for reefer ships, as proposed refrigerant for sorption ice machines, and for fishing vessels both as single refrigerant as well as in combination with CO2 (R744), especially for low temperature uses.
Heat pumps: Absorption heat pumps for hot water space heating are mostly gas-fired and commonly provide cooling simultaneously with heating. An updated family of absorption machines is available using an ammonia-water cycle powered by natural gas. R717 has also been used in medium-size and large capacity heat pumps. In addition, progress has been made in the field of using ammonia for residential heat pumps, with initial prototypes with an output of 6 kW having reportedly worked reliably with ammonia charges of less than 100g.
Leisure industry, Ice Rinks, Ski Slopes: Ammonia can be used for refrigeration purposes in ice rinks and ski Slopes, and in parallel, for the heating of leisure facility premises.. Europe’s largest open air stadium with an ice rink (Karlstad, Sweden), and the world’s third largest indoor snow park (Dubai, Emirates) are both using R717 to constantly produce ice and snow.
14. How Much Ammonia Is Needed For Different Applications?
Large ammonia refrigeration systems contain up to 60,000 kg of refrigerant. Installations for food processing and industrial plant refrigeration typically range from 5 to 100 tonnes. Around the world large R717 systems are subject to increasingly stringent safety regulations and pressure is being placed on companies to reduce the size of ammonia refrigerant charges. Therefore, owners of large industrial plants are starting to use ammonia in conjunction with a secondary refrigerant such as carbon dioxide (R744) or potassium acetate, meaning that an up to 90% reduced ammonia charge is needed compared to an ammonia-only system. The reduction of charge does not lead to any performance compromises.
15. Is Ammonia Compatible With All Components & Materials?
Ammonia is compatible with many, but not all materials suited to synthetic refrigerants. As an example, it is only compatible with some commonly used refrigeration system lubricants, excluding polyol ester (POE) and poly vinyl ether (PVE) lubricants, and it has only limited applications with poly alkylene glycol (PAG) lubricants.
To accommodate for the safety requirements in an R717 system, some modifications to an existing system design might be needed to integrate safety features and ensure compatibility. Ammonia is not compatible with most types of electrical wiring insulation. Metals of construction inside ammonia systems normally are limited to carbon and stainless steel, but good compatibility of ammonia with copper and copper alloys in systems with careful moisture control have been reported, provided that there is no presence of water leading to copper corrosion. Aluminium is compatible with ammonia, but it is sensitive to corrosion in water circuits due to the presence of chlorides.
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16. Are There Any Legal Requirements When Using Ammonia?
The use of ammonia is subject to a wide range of technical and safety standards in different world regions, which, when thoroughly followed, ensure the refrigerant safe and highly efficient use. Workers handling ammonia installations must be knowledgeable of emergency procedures and applicable standards.
In addition, regulations require regular inspection of safety equipment and ongoing training to prepare workers in the event of an emergency, which, compared to other risks in society, are extraordinarily rare. While industry-driven codes and standards include certain system engineering and design standards and operating codes, federal regulations prescribe workplace safety rules when using ammonia, environmental requirements (including reporting and risk management obligations), and transportation rules.
These requirements create regulatory burdens for ammonia refrigeration applications, as facilities have to follow Process Safety Management (PSM) and Risk Management (RMP) Programs linked to paperwork and document retention.
Ammonia systems designed during the past 20-30 years in accordance with pressure vessel legislation and limitations on the amount of ammonia used, are very high quality with excellent standards of safety. For older systems, effective training of personnel with operational responsibilities is worthwile as the most effective low-cost preventive measure.
17. What Are The Key Markets For Ammonia Today?
Industrial Refrigeration: Today, ammonia remains the most cost-effective and energy-efficient option for all types of industrial equipment. In fact, R717 makes up 15% of the total refrigerant market. R717 is expected to remain the preferred choice for large installations once ozone-depleting substances will be ruled out under international agreements. In the US and Canada ammonia is well regulated and enjoys a wide-spread use.
In Europe, R717 has been widely adopted for industrial refrigeration in the UK and Germany but is more tightly regulated in France, Belgium, the Netherlands and Italy, and it is consequently less common. It is the most common alternative to HFCs for larger systems in Scandinavia, mainly as a result of restrictions and taxation on greenhouse gases.
First installations in Australia have proved the efficiency of R717 plants. As a most recent example, ammonia freezes 6000 head of lamb every day in one of Australia’s largest meat processing companies, being capable of freezing 1610 bulk packed export meat cartons with a 24-hour turn around.
Commercial Refrigeration: The use of ammonia in cascade supermarket refrigeration systems is growing, especially in countries with stringent limitations on the use of HCFCs and HFCs, such as Scandinavia.
Chillers: Although the use of R717 is still limited, this market is expected to grow. As a most recent example, a central ammonia chilling plant provides continuous supply of hot and chilled water for heating and air conditioning to Terminal 5 of London’s airport Heathrow.
Heat pumps: R717 has been applied in medium-size and large capacity heat pumps, mainly in Scandinavia, Germany, Switzerland, and the Netherlands.
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18. What Are Major Barriers For A Widespread Use Of Ammonia?
From a purely economic analysis, ammonia should find broader applications as a refrigerant than it currently enjoys. However, to realise ammonia’s full potential as a refrigerant, safety regulations and technical standards around the world will be required to become more tailored to ammonia refrigeration systems and consistent across world markets.
Regulatory restrictions and a lack of clear encouragement from policy makers to move towards natural refrigerants currently impede a wider spread of R717. To sum up, a deficit of promotion, a lack of technical and regulatory harmonization, missing guidance for operators, and a patchwork of national safety regulations pose excessive administrative and financial burden on the ammonia business. Politicians’ recognition of ammonia as a sustainable alternative to ozone-depleting and high global warming substances under international environmental programs could lift these barriers. To achieve this goal, data on the performance and use of R717 has to be updated and spread in coverage to allow for an informed choice.
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19. What Is The Process Of Including Heat Exchanges In Ammonia Refrigeration System?
The heat exchangers are used in ammonia refrigeration system from a very long time. The heat exchanger used is having smaller sizes and they are equivalent to the tubular exchanger can. This process works best for flooded system that require a separate liquid from the vapor. The system that is explained consists of a vessel, a drum, and accumulator and header tank with the heat exchanger. It works like this: >Liquid ammonia moves from vessel to exchanger >Vapor is returned to middle of drum >Vapor is removed from the drum and liquid enters through exchanger as it has lower density than others entering at the same rate in the system.
20. For A Given Bulk Solid How Can The Particle Size Distribution Be Determined?
In order to determine the particle size distribution the simplest method is to make use of a sieve stack. In this method a stack is created of with different mesh sizes at each stack level. The structure is such that the biggest mesh size is at the top and the smallest at the bottom. Once this setup is created the before beginning the weight and other values of the solid is noted down. Once this is done the solid is placed at the topmost cylinder and the entire setup is exposed to a combination of vertical and horizontal movements. This will make the solid pass through different mesh sizes in the process separating the different particles according to their sizes. There are other more advanced methods of determining the particle size distribution as well such as video imaging and laser diffraction as well.
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21. In A Crusher Where Is The Energy Provided To It Is Used Up For?
The energy fed to a crusher is utilized for the following purposes:
To produce the elastic deformation of the particles prior to the fracture of the particles.
In order to produce inelastic deformation this causes the particles to reduce in size.
The energy is also used to cause the equipments elastic distortion.
In the friction of the particles between themselves and between the machine.
The energy also gets used up in the form of heat, noise and vibration in the plant.
The energy also gets used up in the friction losses in the plant. Most of the energy is lost and only some of it is properly utilized. Nowadays it is of prime importance to reduce the energy losses.
22. In Case Of Welded Vessels Why Is Stress Relieving In The Form Of Post-weld Treatment Necessary?
When a metal is welded together the point at which the two surfaces are joined are subjected to very high temperatures. During this time period the metals can go through a lot of random metallurgical processes. This causes the metal to be harder and brittle. This depends on the amount of carbon content. In order to relieve the metal of these properties heat treatment is done on the affected areas. By doing so the affected areas ductility increases. In this process the heat is maintained in the affected metal according to the thickness of the metal. The temperature of the heat is calculated from the P number which is unique for a particular composition.
23. Mention Some Of The Specialized Grinding And Crushing Methods?
Some of the specially developed grinding and crushing methods are as follows:
Electro hydraulic crushing: In this method an underwater discharge is created from a high capacity capacitor.
Ultrasonic Grinding: This type of grinding the material id placed between a drive roll and plate both of which are ultrasonically activated. This process is used for grinding micro sized materials.
Cryogenic grinding: For certain materials effective grinding is not possible by conventional means such as rubber, textiles etc. In order to cope with this problem the material is frozen to ultra low temperatures using liquid nitrogen. Once the material is frozen it is grounded as per requirements.
Explosive Shattering: This type of shattering is still on experimental basis, it involves energy to be transmitted to the particles in the form of shockwaves from an explosion chamber.
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24. On What Basis Are Materials To Be Crushed Evaluated Apart From Size?
The choice of the crusher machine to be employed to crush the materials depends on the following properties apart from the size of it:
Hardness: The hardness affects the power consumption and the wearing of the machine. With hard materials it is necessary to use a low speed machine along with pressure lubrication.
Structure: Normal granular materials can be crushed by using compression and impact methods. On the other hand for fiber like materials compression and impact methods don’t work instead a tearing action is required.
Moisture content: The moisture content in the materials can greatly affect the choice of machines. In case of excess moisture the materials flow gets hindered and it is essential to prevent them from caking together and form balls.
Crushing Strength: The amount of power that is required to crush a material can be derived directly from the crushing strength of the material.
Friability: This property indicates the tendency of a material to fracture.
Stickiness: As the name suggests this property is used to evaluate how sticky a material is as a very high sticky material can clog the machinery.
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25. What Are The Advantages Of Using A Ball Mill Over Other Conventional Methods Of Crushing?
The advantages of using a ball mill over other conventional methods are as follows:
The mill can be used in multiple modes. It can be used in both wet and dry modes. The wet mode helps in the removal of the product.
The installation cost and the power consumption of the mill is low.
Since the mill can be used in an inert atmosphere hence it would be used for the crushing of explosive materials.
It can be used for any type of hardness materials and also the grinding medium is cheap.
It can also be used for continuous and batch operations.
The ball mill supports two types of grinding:
Open circuit grinding.
Closed circuit grinding.
26. What Are The Assumptions Made For Kynch Theory?
The following assumptions are made for the Kynch Theory:
Across the horizontal layer the particle concentration is uniform.
The effects of the wall can be ignored.
No differential settings of particles are considered due to shape, size or composition changes or differences.
The velocity at which particles fall depends only on the local concentration of the particles and nothing else.
The concentration is considered to be uniform throughout or it can be assumed to increase towards the bottom.
The velocity of sedimentation approaches zero as the concentration reaches the limiting value.
This limiting value corresponds to the sediment layer at the bottom which gets deposited.
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27. What Are The Assumptions Made On Conservation Equation?
The conservation equation is applied to the property of the system.
It can have complicated as well as easy to solve calculations:
Closed system: That doesn’t have flows out of the substance. It deals with the closed mass flow.
The equation to calculate this is:
Accumulation= Generation > Open system: that allows the substance to enter or leave the system.
Conserved state system: in which no generation of the quantities happens. The quantities in this doesn’t get created or destroyed. These quantities are useful to balance according to the users need.
Steady State system: in which no accumulation of the substance is in steady state. This system avoids having differential equations. The process needs to be validated before it can run in any state.
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28. What Are The Criteria Involved In Choosing Mass Balances For Components?
The mass balances are used to combine all the masses that are present in the substance and create an overall effect when it is combined with other factors. The equations can be set for the component to allow any of the components used in mass balances.
The criterias on which the balances are dependent are as follows:
Need to find out which component(s) are involved in solving the equations, without proper information the equation can`t be solved.
Find out about the components about which the reasonable assumptions can be made. By doing this the process gets simplified and it will help in making quick calculations.
29. What Are The Design Considerations For A Piping System For The Transfer Of Slurries?
The following points must be considered for designing a piping system to carry slurries:
The design of the piping system should be able to self drain.
At the sections of the pipe where self draining is not possible provision to install manual draining must be installed.
At certain points where the chances of plugging are high, rod-out or blow-out connections must be provided to clear the lines.
In order to make flushing possible clean-out connections should be installed on either side of the main valves.
For easy access all the manifolds should have flanged connections.
T-connections are a must for access flanges.
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30. What Are The Different Characteristics That Can Affect The Flow Of Bulk Solids And How?
The main characteristics that can affect the flow of bulk solids are as follows:
Moisture Content: when the moisture content is high the bulk solids become sticky in nature. This moisture can sometimes be absorbed from the atmosphere by some solids.
Temperature: The flow of the bulk solids can be sometimes affected by the temperature and also the period for which it is exposed to a particular temperature.
Particle size: More cohesive particles are generally found in bulk solids that are finer. Round particles are handled easily in comparison to odd, asymmetrical shapes.
Time at rest: Many times the flow of certain bulk solids is affected by the time for which it has been kept stagnant or at rest. The more it is kept at rest the more slow the bulk solid flows.
31. What Are The Different Types Of Equipment For The Conveyance Of Solids?
The various types of equipments available for the conveyance of solids are as follows:
Gravity Chutes: This equipment relies on gravity for the solids to fall under.
Air Slides: In this equipment the particles are suspended in air, and flow at an angle to the horizontal.
Belt Conveyors: This equipments use a belt to transfer the solids.
Screw Conveyors: The solids are moved using a rotating helical impeller.
Bucket elevators: The solids are moved using buckets which are attached to a belt in motion.
Vibrating Conveyors: The solid particles are subjected to vibrations and travel over to a table in a series of steps.
Pneumatic/ Hydraulic Installations: The particles are transported over a stream of air or water.
32. What Is The Different Ways In Which Solids Can Be Blended?
There are various ways in which solids can be blended, some of the common methods are:
Convective mixing: In this type of mixing the group of particles of a solid is transferred from one place to another, vigorous repositioning takes place in this method. This type of mixing is prevalent in the Trough mixer.
Diffusion mixing: In this type of mixing a new interface is formed over which the particles of a solid are distributed. A good example of diffusion mixing is in the traditional barrel mixer, where a new interface is formed.
Shear Mixing: In this type of mixing slipping planes are created over which the group of particles of a solid are mixed.
33. What Are The Factors Involved In Considering The Choice Of Dry Screw Compressor?
Screw compressors are made up of a pair of meshing helical screws that is used to compress the gases. The dry screw compressors are used to have a flow range of 85-170 m/h and the discharge pressure is of 2070-2760 kPa. The dry screw compressor consists of timing gears that is maintained aligned with the rotors. The effectiveness is dependent on the clearances that exist between the helical rotors and between the chambers used for sealing the compression cavities. They are compact and smooth having the limited vibration and require spring suspension as well.
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34. What Are The Factors Involved In Designing Kettle Type Reboiler?
To design the kettle type reboiler the requirements that needed to be present are as follows:
The size of the kettle has to be determined.
Provide the space to slow down the vapor velocity of all the liquid droplets.
Deciding the destination where the vapor would be deposited.
Handling a distillation tower with the following property: large space, high efficiency and high reflux rate.
The height of the vapor space should be kept such that the differences in the temperature won’t affect the kettle.
There should be high heat flux for the kettles that run on higher temperatures.
35. What Are The Merits Of Using A Falling Film Evaporator?
The advantages of using falling film evaporators are as follows:
These types of evaporators have very high heat transfer coefficients ranging from 2000-5000 W/m(square) for water and 500 to 1000 for organic liquids.
The residence times are short in case of heated surfaces, 5-10 seconds without recirculation.
They have very low pressure drops, 0.2-0.5 kN/m(square).
These evaporators are well suited for vacuum operations as well.
The evaporation ratios are very high. 70 per cent without and 95 per cent with recirculation.
They have a very wide operating range, they can provide as much as 400% of the minimum throughput.
In addition to the above advantages they have a low cost of operation and are less susceptible to fouling.
36. What Are The Methods Involved To Test Helium Leak Testing In A Vacuum System?
The helium gets detected when it is found in the location of suction line. The helium source is passed over the flanges and possible sources of leakage in the vacuum system. The monitoring of the system takes place to see the detector and the pump suction to be found for the detectable amount of helium. The pressure can be increased or decreased according to the environment. If the system is allowing the pressure and the vacuum at the same time then more pressure can be applied to set the leaks. An installation of IR unit can be done to suction the substance of the pump and the spraying will be done on the flanges.
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37. What Are The Problems That Are Associated With The Expansion Joints?
Expansion joints are said to be weak points that are used in piping. They are used to reduce the stress that comes in the piping while installing and implementing it. This allows minor piping to be settled during the joining function. Expansion joints can’t stand the stress that is being produced by the piping forces.
The problems that have been given are as follows:
Expansion joints get dirty very easily and they tend to build up as the time progresses.
They include some weak points that can`t stand the stress of the piping.
The issues can be removed if the drains are installed properly and purging of the material is being done.
38. What Are The Reasons Of Removal Of Particles From Effluent Gas?
The main reasons for the removal of particles from effluent gas are:
In order to protect and maintain the health of the workers and operators in the plant. It is also done to protect the surrounding population. The primary danger is due to the inhaling of the dust particles which can cause health issues.
It is also done to minimize the chances of explosions. Many carbonaceous materials remain suspended in air and when mixed with finely powdered metals can form a highly combustible mixture.
Particles are also removed to reduce the loss of valuable materials.
It can also be used to recycle the gas for ex in case of blast furnaces the gas is used to fire the stoves.
39. What Are The Steps Required To Design A Vapor-liquid Separator Or Flash Drum?
The steps that are required are as follows:
The size of the vapor-liquid separator depends on the flow rate of vapor and the liquid that is coming out of the vessel.
Assumed from the flow rates that if they are known then the size can be found out.
Use vertical pressure vessel to set it up or install it at given location.
The length to diameter ratio will be taken to provide liquid inventory between the level of liquid and the bottom of the vessel.
Provide a blockage mesh section at the vapor outlet to let the vapor pass through the mesh that is taken and can successfully leave the vessel.
Let liquid flow control the level of the valve.
40. What Are The Steps Taken To Operate A Tank-blanketing Valve?
The steps taken are as follows:
Tank blanketing valves provide a way to prevent and control the fires in the flammable liquid storage tanks.
The vapors that are produced cannot be ignited if there is no supply of oxygen present at that time.
The oxygen in most of the cases being provided by the air that is drawn into tank from the atmosphere when the empty process is taking place.
Install tank blanketing valves with inlet connected to the inert gas that is kept under the pressure. And the tanks outlet is being placed in vapor space.
The pressure drop is happening in the tank at predetermined level where the blanketing valve allows the transfer of gas into vapor space.
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41. What Are The Strategies Acquired To Cure Tube Vibration And Exchangers In A Shell?
The strategies that can be followed are as follows:
To cure the tube vibration uses the tubes that doesn’t allow passing of the flow-induced vibrations through them and are longer in height than others. Usually the tubes supported >Are of 3-4 inch. To make the bundle stiff insert metal slats and rods between the tubes that is used in the process.
Add a shell nozzle opposite of the inlet to cut the flow of the velocity of the fluid in half. This solution works for non-removable bundles that can easily be solved also by adding a distributor belt on the shell. This might be expensive solution to adopt as it requires more man power and use of more tubes.
42. What Do You Understand By Wet Bulb Globe Temperature?
The wet bulb globe temperature index is used to measure the sultriness of the environment. The sultriness is calculated on the basis of the humidity affects, the air speed and temperature and also the sun`s radiant heating factor. The sultriness in some cases could be fatal and hence it is very important to keep this under consideration. The wet bulb globe temperature index number was developed in the 1950`s and is now accepted as an industry standard.
It is comprised of three temperature readings:
Wet bulb temperature
Ordinary dry bulb temperature
Black bulb globe temperature
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43. What Is The Method Adopted To Minimize Shell Side Pressure Drop In A Shell?
The method of protecting the shell from the pressure drop is very essential as it is very critical stage, where if not taken care properly the shell has to be replaced due to its degradation. In this rods or tube protectors are used instead of plates in top rows. The use of these rods puts less pressure drop and provides better distribution of the pressure on the plate. The plate that is used causes an abrupt of 90 degree turn of shell stream and an extra pressure drop on the whole shell. Use of the tube protectors will allow the shell to be saved from this and maintains its longevity.
44. What Is The Method Involved In Analyzing Powders For Composition?
The method that is used to analyze powders for compositions called as Fourier transform-infrared spectroscopy. This method is widely used to send the light beams of varying wavelength passing through the sample that is given and the light that is reflected from there will be analyzed by spectroscopy. This method is used to find out the absorption of each wavelength. The wavelength is measured with the laser light that is being referenced and on the basis of that calculations will be performed. The method is adopted to measure the compositions with accuracy.
45. What Is The Procedure To Estimate The Friction Factor Involved In Heat Exchanger Tubes?
The following procedure is involved in determining the factors used inside the heat exchanger tubes that are varying with the temperatures.
These are as follows:
Determine the average of the temperature by taking the mean of all the temperatures stored in the processing line.
Check the condition of the fluid entering the line at around 300 Celsius and leaving at around 280 Celsius.
Determine the physical properties at the temperature of 290 Celsius and the friction factors of the tubes at the same temperature.
Use the formula to calculate the friction factor of the laminar flow in the case where the liquid is cooling: Mean temperature/((sum of viscosity/wall viscosity)*0.38) Where Bulk and wall is determined at mean temperature over the length of line.
Use the formula to calculate the friction factor of the turbulent flow in the case where the liquid is cooling:
(Mean temperature + bulk properties / ((sum of viscosity/wall viscosity)*0.11))/ (bulk viscosity/wall viscosity)*0.17.
46. What Is The Process Of Including Heat Exchangers In Ammonia Refrigeration System?
The heat exchangers are used in ammonia refrigeration system from a very long time. The heat exchanger used is having smaller sizes and they are equivalent to the tubular exchanger can. This process works best for flooded system that require a separate liquid from the vapor. The system that is explained consists of a vessel, a drum, and accumulator and header tank with the heat exchanger.
It works like this:
Liquid ammonia moves from vessel to exchanger.
Vapor is returned to middle of drum.
Vapor is removed from the drum and liquid enters through exchanger as it has lower density than others entering at the same rate in the system.
47. What Is The Use Of Gear Pumps In Motor?
Gear pumps uses meshing gears that allow the pump fluid to be displaced by the method of displacement. They are used for hydraulic fluid power applications. They are one of the key factors involved in chemical installation having a certain viscosity to pump fluid. This type of pumps uses positive displacement pump having high pressure and low capacities. This includes the ability to handle wide range of viscosities, and allow easy to build and maintain the pumps. The gear pumps are controlled through the motor speed. Gear pumps can’t handle high tolerances and the fluids that are free of abrasives.
48. What Significance The Angle Of Repose Holds In The Chemical Industry, Explain?
The angle of repose is a property of particulate solids. A conical pile is formed when a bulk solid is poured onto a flat surface. The angle formed between the flat surface and the pile edge is called the angle of repose.
The angle of repose depends on the following factors:
Density of the material
Coefficient of friction of the material A material having a low angle of repose would always create float piles as compared to materials with a high angle of repose. This is used in the designing of equipments which are used for particulate solids. In addition to that this angle can be used to calculate the size of the conveyor belt that is used to transfer the materials.
49. Why Does Catalytic Converter Used In An Automobile?
The catalytic converter is a device that converts harmful compounds in harmless compounds.
The compounds harmful in nature are as follows:
Hydrocarbons- this is in the form of unburned gasoline that creates pollution and is more harmful.
Carbon monoxide is very harmful gas formed by the combustion of gasoline and used mainly for fuels.
Nitrogen oxides is also one of the gases that is poisonous in nature and produced by the release of heat from the engines. The release of nitrogen from the engine gets mixed with the oxygen in the air. The catalyst converter takes these harmful gases and uses the catalyst that is coated on the ceramic honeycomb or beads and attached to the exhaust pipe. This converts the carbon monoxide in carbon dioxide and makes it easy for the nature to consume it. The hydrocarbon gets converted in carbon dioxide and water. Same way the nitrogen oxides also gets converted in nitrogen and oxygen.