Chapter 2 Steam, Air & Inert Gases Plant Utilities PDF

CHAPTER-2 Steam, Air & Inert Gases Plant Utilities For 3rd Sem For 1st Sem Course Outcome: Course Outcome: 4330505.2:Explain Different Types of Steam Generators and Compressor...

CHAPTER-2 Steam, Air & Inert Gases Plant Utilities For 3rd Sem For 1st Sem Course Outcome: Course Outcome: 4330505.2:Explain Different Types of Steam Generators and Compressors along with their CO.2- Operate various steam generators, components. compressors and blowers. 4330505.4: Apply concepts of energy efficiency and green chemistry for conservation of CO.4- Apply concepts of energy efficiency and utilities. green chemistry for conservation of utilities. Uses of steam In steam engine and steam turbine, In power generation It is used as the working substance in the operation of steam engine and steam turbine. As of around 90% of all electricity was generated using steam as the working fluid, nearly all by steam turbines. For Heating purpose- steam is used as the heating source for process fluid heat exchangers, reboilers, reactors, combustion air preheaters, and other types of heat Shell and Tube Heat Exchanger Jacketed reactor transfer equipment.  In vacuum generation- steam jet ejector Steam is used as Motive Fluid to generate steam in steam jet ejector.  For Pipe tracing- Steam is used in piping for utility lines. It is also used in jacketing and tracing of piping to maintain the uniform temperature in pipelines and vessels.  In agriculture, steam is used for soil sterilization to avoid the use of harmful chemical agents and increase soil health. For Drying- Steam is also used to dry and eliminate the moisture content in the products. for Sterilization and Disinfection For atomization For Cleaning- steam used to remove dry ash and slag. For Moisturization- for example Pulp and paper industry, For Humidification  Uses of Compressed air When air is required at comparatively low pressure, Higher than (> 4 Kg/cm2 Compressed air is used. Process air - air used in reaction, for example oxidation In instrumentation and control valve; used to operate various control valve Material handling and conveying– air is used in controlled pneumatic pumping system. To transfer solids Nitrogen production unit - in a variety of chemical applications. Product drying –hot air is used to dry products and speed up drying process. Air curtains-Compressed air is used as a curtain to create a safe and clean area. Blower air When air is required at comparatively low pressure, 1.5 to 4 kg/cm2 Blower air is used. Application/Uses combustion process, supply of oxygen To remove fumes of HCL, Cl2 etc Fan air When air is required at low pressure, 0.5 to 1.5 kg/cm2 but in high volume. Application/Uses Ventilation Drying Instrumental Air The term “Instrument Air” refers to an extremely clean supply of compressed air that is free from contaminates such as moisture & particulates. Uses: A system may utilize instrument air for various types of pneumatic equipment, valves & electrical controls. Used in a facility to operate valves and certain types of pumps. Pneumatic actuators rely on instrument air for operation. Some types of modulating valves require instrument air for throttling. Industry Example Compressed Air Uses Automotive Tool powering, stamping, controls and actuators, forming, conveying Chemicals Conveying, controls and actuators Dehydration, bottling, controls and actuators, conveying, spraying coatings, Food cleaning, vacuum packing Furniture Air piston powering, tool powering and cleaning, controls and actuators General manufacturing Clamping, stamping, tool powering and cleaning, controls and actuators Lumber and wood Sawing, hoisting, clamping, pressure treatment, controls and actuators Assembly station powering, tool powering, controls and actuators, injection Metals fabrication molding, spraying Primary metals Vacuum melting, controls and actuators, hoisting Rubber and Plastics Tool powering, clamping, controls and actuators, glass blowing and molding, cooling Conveying, blending, mixing, controls and actuators, glass blowing and molding, Stone, Clay and Glass cooling Agitating liquids, clamping, conveying, automated equipment, controls and Textiles actuators, loom jet weaving, spinning, texturizing Service Pneumatic tools, hoists, air brake systems, garment pressing industries machines, hospital respiration systems, climate control Power Starting gas turbines, automatic control, emissions controls generation  Properties of Steam Enthalpy: The term formerly known as sensible heat, latent heat and total heat of steam are known as the enthalpy of water enthalpy of evaporation and enthalpy of saturated steam respectively. Similarly the term total heat of superheated steam is now known as “enthalpy of superheated steam”. Enthalpy of evaporation is the difference between enthalpy of dry saturated steam and enthalpy of saturated water. Enthalpy of evaporation = ( Enthalpy of dry saturated steam) – (Enthalpy of boiling water)  Enthalpy of water The amount of heat absorbed by 1 kilogram of water is being heated from freezing point (0oC) to the boiling point ts is known as the enthalpy of saturated water (sensible heat of water) and is denoted by a symbol H To rise the temperature 1 kg of water from 0oC to 100 oC requires 4.187*100 = 418.7 kJ. Hence, this number is the enthalpy of 1 kg of water at 100 oC.  Enthalpy of Evaporation The enthalpy of evaporation or latent heat is defined as the amount of heat required to convert 1 kilogram of water at a given temperature ts and pressure „P‟ into steam at the same temperature and pressure. The value of enthalpy of evaporation varies with the pressure. It is usually expressed by the symbol „L‟ and its value at 1 bar is 2258 KJ per kg. The value of enthalpy of evaporation of latent heat of 1 kg of dry saturated steam can be directly obtained from the steam tables.  Enthalpy of dry saturated steam It is the sum of enthalpy of saturated water and enthalpy of evaporation. It is defined as the quantity of heat required to raise the temperature of 1 kilogram of water from freezing point to the temperature of evaporation ts and then convert it into dry saturated steam at that temperature and pressure. It is denoted by symbol „Hs‟. The enthalpy of 1 kg of dry saturated steam Hs Enthalpy of saturated water + Enthalpy of evaporation Hs = h + L ….. KJ/kg The value of enthalpy Hs of 1 kg of dry saturated steam can be directly obtained from the steam tables corresponding to given value of pressure or temperature. Enthalpy of evaporation is the enthalpy difference between dry saturated steam and saturated water. Wet steam The steam in the steam space for of a boiler generally contains water mixed with it in the form of fine water particles. such a steam is known as a wet steam. The quantity of steam as regards its dryness is termed as dryness fraction. Dryness fraction of wet steam is the ratio of the mass of actual dry steam to mass of wet steam containing it. The dryness fraction is usually expressed by the symbol x. dryness fraction is often spoken as the quality of wet steam If ms = Mass of dry steam contained in steam m = Mass of water in suspension in steam Then, Dryness fraction, x= (ms/( ms + m)) Thus, ‘f’ dryness fraction of wet steam x= 0.8, then one kg of wet steam contains 0.2 kg of moisture in suspension and 0.8 kg of dry saturated steam.  Superheated Steam If the steam remains in intimate contact with water during its formation, interchange of molecules between the water and steam will result. This interchange of molecules will continue as long as there is any water in the cylinder. This will not allow the steam to become dry. If water is entirely evaporated and further heat is then supplied, the first effect on the steam is to make it dry if it is not already dry the temperature. The temperature of steam will then begin to increase with a corresponding increase in volume. steam in this condition, heated out of contact with water, is said to be superheated. superheating is assumed to take place at constant pressure. The amount of superheating is measured by the rise in temperature of the steam above its saturation temperature ts. Greater the amount of superheating, the more will the steam acquired the properties of a perfect gas. Heat absorbed per kg of dry steam during superheating = Kp (tsup - ts) kJ/kg Where tsup = Temperature of superheated steam ts = saturation temperature at the given pressure Kp = Mean specific heat of superheated steam at constant pressure Enthalpy of one kg of superheated steam, Hsup = Hs + Kp (tsup - ts) kJ/kg Where , Hs = The enthalpy of 1 kg of dry saturated steam Specific volume of steam The volume of 1 kilogram of dry saturated steam at all pressures is given in column 3 of the steam tables. The volume in cubic metre per kg of dry saturated steam (m3/kg) is known as the specific volume of dry saturated steam and its symbol is Vs. Specific volume of wet steam, having a dryness fraction of x = Volume of dry steam + Volume of water particles = x Vs + (1 – x) Vw Where Vs and Vw are the specific volume of steam and water respectively. The approximate specific volume of superheated steam may be calculated as Vsup = Vs * (Tsup/Ts) m3/kg Where ‘ Tsup’ is the absolute temperature of superheated steam, ‘Ts’ is the absolute saturation temperature of steam and ‘Vs’ is the specific volume of dry saturated steam. CLASSIFICATION OF STEAM GENERATOR  Comparison FIRE TUBE BOILER WATER TUBE BOILER Hot flue gases flow inside the tube and the water Water flows inside the turbine and hot flue gases outsides the tubes. outside the tube. These boilers are generally internally fired. These boilers are generally extra really fired. The boiler pressure limited to 20 bar. The boiler pressure is limited to up to 100 bar. The fire-tube boiler has a lower rate of steam A higher rate of steam production. production. Not suitable for larger power plants. Suitable for larger power plants. Involves lesser risk of explosion due to low The risk of the explosion is higher due to high pressure. boiler pressure. For a given power, it occupies large floor space. For a given power, it occupies small floor space. This boiler is difficult to construct. Simple in construction.  FIRE TUBE BOILER WATER TUBE BOILER For a given power, it occupies large floor For a given power, it occupies small floor space. space. This boiler is difficult to construct. Simple in construction. It is simple in design. It is complex in design. But the Water tube boiler has High This is having a low maintenance cost. maintenance cost. Fire Tube Boiler example: Water Tube boiler example: Cochran Boiler Benson Boiler Cornish Boiler Lamont Boiler Locomotive Boiler Babcock and Wilcox Boiler Velcon Boiler Lamont Boiler Simple Vertical and Loeffler boiler and Scotch Marine Boiler. Yarrow boiler.  Boiler mountings Boiler accessories They are mounted on the surface of the The accessories are the integral parts of the boiler. boiler. Boiler mounting’s function is to ensure safe Boiler accessories function is to increase the and smooth working of the boiler. efficiency of the boiler. A boiler cannot function without boiler A boiler can function without boiler mountings accessories. Boiler mountings are mounted onto the They are not mounted onto the boiler shell. boiler shell. Boiler mountings are related to the safety of Boiler accessories are related to the the boiler. performance of the boiler. Examples of boiler mountings include Water level indicator, safety valve, feed valve, Examples of boiler accessories include Air blow-off cock, fusible plug, steam pressure preheater, economizer, superheater, etc. gauge, etc. Boiler Mountings: As the name mountings, in the sense, they are mounted on the surface of the boiler. The mountings are the parts without which the boiler operation is not possible. Boiler mountings are components used for ensuring the safety of boiler operation. These are generally mounted on the surface of the boiler. MR. P.D. PRAJAPATI  1. Safety valve: It is used to blow off the steam when the pressure of the steam inside the boiler exceeds the working pressure. The boiler safety valve is designed to come into action to release the overpressure. The function of a safety valve is to prevent excessive pressure from building up in a steam boiler. The safety valve also warns the boiler attendant as the steam escape through the safety valve..  2. Water level indicator: It indicates the level of water in the boiler. It is placed in front of the boiler. Two water level indicators are used in the boiler. Enable the attendant to regulate the supply of feed water in the boiler to maintain correct level.  3. Pressure gauge: The function of the pressure gauge is to indicate the pressure of the steam inside the boiler.  4. Steam stop valve: Its function is to stop and allows or regulate the flow of steam from the boiler to the steam pipe.  5. Feed check valve: It stops and allows the flow of water inside the boiler. To control the supply of feed water to the boiler from the feed pump and To prevent any water escaping back from the boiler in the event of failure of the feed pump or the pump pressure less than the boiler side.  6. Blow off cock: Its function is to remove the sediments or mud periodically that is collected at the bottom of the boiler. (i) To blow out sediments, precipitated sludge, loose scale or other impurities periodically when the boiler is in operation. (ii) To empty the boiler when necessary for cleaning, repair and inspection. (iii) To permit rapid lowering of water level in the boiler if accidentally it becomes too high.  7. Man hole: it is a hole provided on the boiler so that a man can easily enters inside the boiler for the cleaning and repairing purpose. 8. Fusible plug: it is used to extinguish the fire inside the boiler when the water level inside the boiler falls to an unsafe level and prevent explosion. It also prevents the damage that may happen due to the explosion. The function of the fusible plug is to protect heating surface area of the boiler against damage of overheating when the water level in the boiler falls below the safe limit.  9. Grate: it is a platform which is used to burn the solid fuel. 10. Fire door: it is used to ignite the fuel present inside or outside the boiler. 11. Ash pit: it is used to collect the ash of the fuel after the fuel is burnt. Boiler Accessories: Accessories are the auxiliary items required for proper operation of boiler and improve the Boiler efficiency of it. These are integral parts of the boiler, but not mounted on it. Control fluid parameters at outside of the boiler. These are not essential parts of the boiler, without which boiler can operate through at lower efficiency. 1. Economizer: It is a mechanical device which is used as a heat exchanger in steam power plant. It is used to pre-heat the fluid or water by taking the residual heat from the combustion products i.e. flue gases. it is just installed to increase the efficiency of the boiler in the power plant. the Energy improving device that helps to reduce the cost of operation by saving the fuel. the exhaust gases which are leaving the Boiler at such high temperature is made to pass through the Economiser in order to provide the required sensible heat to the water by increasing its temperature, it will reduce the heat load on the boiler to the greater extent. 2. Air pre-heaters: It is a mechanical device which abstracts the heat from the flue gases and transfers it to the air. In boilers the pre-heaters are installed in between the economizer and the chimney. The air preheater is an accessory that recovers the heat in the exhaust gas by heating the air supplied to the furnace of the boiler. Supplying preheated air into the furnace produces a high furnace temperature and accelerates the combustion of the fuel. Thus the thermal efficiency of the plant will be increased. Advantages Increase in the steam generation rate. Better combustion with less soot, smoke and ash, and Low-grade fuels can be used. 3. Superheater The superheater is used in boilers to increase the temperature of the steam above the saturation temperature. The superheater raises the temperature of saturated steam without increasing its pressure. It consists of a small bundle of tubes. It is set in the path of the hot flue gas of the furnace. Saturated steam passes inside the heater tubes, and hot flue gases pass outside the tubes. Thus the transfer of heat takes place in saturated steam from hot flue gases and raises its temperature without increasing the pressure of steam.  Advantage of Superheater Steam consumption reduced. Protection from turbine corrosion. The losses from the condensation of steam in cylinders and pipes are reduced. Increases efficiency of plants. Condensate Condensate is the liquid formed when steam passes from the vapor to the liquid state. Steam that has been condensed back into water by either raising its pressure or lowering its temperature. Where does condensate come from? Condenser hotwells, the bottom part of the condenser Steam traps. They trap steam in the lines and let the condensate drain through. Heat Exchangers. Condensate must be removed to allow the Heat Transfer. The condensate flows to the bottom where the steam trap will open and allow the condensate to flow to the receiver. There must be a positive differential pressure between the Heat Exchanger and the condensate line so that the condensate will flow out of the Heat Exchanger. If the differential pressure is not there, a pump will have to be installed to remove the condensate. Or any other place that you are using steam.  Condensate in the transport piping accumulates on the bottom of piping, and then pushed in the flow direction of steam by the steam which flows at high-speed. If condensate removal is insufficient, the wave of condensate in the bottom becomes higher and higher, and then arrive at the peak of piping finally, and condensate which become piston-like is pushed by steam, and advances at high speed. When this collides with a valve or a pipe bend part, big sound and vibration are produced. This phenomenon is called as water hammer. This may produce not only noise but joint loose to cause leak or may destroy a valve. To prevent such water hammer, sufficient condensate removal is required.  The key to consistent and efficient heat transfer from process steam is efficient condensate removal  Steam trap Steam traps are a type of automatic valve that discharge out condensate (i.e. condensed steam) and non-condensable gases such as air without discharging the steam (letting steam escape). The purpose of installing the steam traps is to obtain fast heating of the product and equipment by keeping the steam lines and equipment free of condensate, air and non-condensable gases. A steam trap is an automatic valve that allows condensate, air, and other non-condensable gases (CO2) to be discharged from the steam system while holding or trapping the steam in the system. So, Steam Traps separate out the condensate from the mixture. Functions of Steam Traps The three important functions of steam traps are: To discharge condensate as soon as it is formed. Not to allow steam to escape. To be capable of discharging air and other incondensable gases.  Condensate: Condensate forms whenever steam releases its heat energy for any reason. Air: Air exists in all steam pipes prior to system start-up when the system is cold. Air can enter the system through boiler water make-up systems and vacuum breakers. Non-Condensable gases: Gases other than air such as carbon dioxide exist inside steam systems.  Advantage of steam trap Minimal steam loss. Long life and dependable service without Rapid wear. Corrosion resistance to fight the damaging effects of acidic or oxygen-laden condensate Air venting for efficient heat transfer and to prevent system binding CO2 venting to prevent the formation of carbonic acid. Operation against back pressure Types of Steam Traps Thermostatic (operated by changes in fluid temperature) The temperature of saturated steam is determined by its pressure. In the steam space, steam gives up its enthalpy of evaporation (heat), producing condensate at steam temperature. As a result of any further heat loss, the temperature of the condensate will fall. A thermostatic trap will pass condensate when this lower temperature is sensed. As steam reaches the trap, the temperature increases and the trap closes. Mechanical (operated by changes in fluid density) – This range of steam traps operates by sensing the difference in density between steam and condensate. These steam traps include 'ball float traps' and 'inverted bucket traps'. In the 'ball float trap', the ball rises in the presence of condensate, opening a valve which passes the denser condensate. With the 'inverted bucket trap', the inverted bucket floats when steam reaches the trap and rises to shut the valve. Both are essentially 'mechanical' in their method of operation. Thermodynamic (operated by changes in fluid dynamics) – Thermodynamic steam traps rely partly on the formation of flash steam from condensate. This group includes 'thermodynamic', 'disc', 'impulse' and 'labyrinth' steam traps.  Compressor A compressor is a mechanical device that increases the pressure of a gas by reducing its volume. An air compressor is a specific type of gas compressor. An air compressor is a device that converts power (using an electric motor, diesel or gasoline engine, etc.) into potential energy stored in pressurized air (i.e., compressed air). By one of several methods, an air compressor forces more and more air into a storage tank, increasing the pressure. Types of air compressor  Positive displacement Compressor A positive displacement compressor is the system which compresses the air by the displacement of a mechanical linkage reducing the volume. Positive displacement compressors draw air into a compression chamber, then reduce the size of the compression chamber to achieve the desired air pressure. The various positive displacement compressor types use different mechanical movements to achieve the compressed air. Positive displacement compressors are divided into those which compress air with a reciprocating motion and those which compress air with a rotary motion. The principal types of positive displacement compressors are the piston, diaphragm, rocking piston, rotary vane, lobed rotor, and rotary screw. Reciprocating Air compressor Rotary Air compressor Reciprocating compressor  Reciprocating compressor Reciprocating Air Compressor is a positive displacement air compressor in which air is sucked in a chamber and compressed with the help of a reciprocating piston by a crankshaft to deliver gases at high pressure. It is called as positive displacement compressor because air is first sucked in a chamber and then compression is achieved by decreasing area of the chamber. The area is decreased by a piston which does reciprocating motion. The intake gas enters the suction manifold, then flows into the compression cylinder where it gets compressed by a piston driven in a reciprocating motion via a crankshaft, and is then discharged.  Main Parts: Piston: It does reciprocating motion in the cylinder and responsible for the compression of the air. Cylinder: It is a chamber in which air is compressed. Connection Rod: It connects the piston and crankshaft. Crankshaft: It is connected to the shaft of electric motor. And transfers its rotary motion to the piston. Suction valve: The air is sucked through suction valve when piston moves to BDC. Discharge valve: The compressed air is discharged through the discharge valve to the storage tank.  Types of Reciprocating Air Compressor Reciprocating Air Compressor has also classified according to its stages. So, Classification will help you better understand the working of the reciprocating air compressor. The principle of operation is same in each type. But according to stages, the building of discharge pressure is different in each compressor. 1. Single Acting reciprocating air Compressor 2. Double Acting reciprocating air Compressor 3. Single stage reciprocating air Compressor 4. Double stage reciprocating air Compressor 5. Multi stage reciprocating air Compressor  Single Acting Reciprocating Air Compressor In single acting reciprocating air compressor only single side of the piston is used for the compression of the air and other side is connected to the crankcase and not used for the compression.  Double Acting Reciprocating Air Compressor In this types of compressor, both the sides of the piston is used for the compression of the air. When suction takes place at one side than compression is taking place at other side. Both suction and compression takes place on each stroke of the piston. Single Stage Reciprocating Air Compressor Double Stage Reciprocating Air Compressor  First of all fresh air is sucked from atmosphere in low pressure (L.P.) cylinder during its suction stroke at inlet pressure p1 and Temperature t1. 2). The air after compression in L.P. cylinder (1st stage) from 1 to 2 is delivered to intercooler at pressure p2 and Temperature t2. Now air is cooled in intercooler from 2 to 3 at constant pressure p2 and from Temperature t2 to t3. After that air is sucked in high pressure (H.P.) cylinder during its suction stroke. Finally air after further compression in H.P. cylinder (i.e. second stage) from 3 to 4 is delivered by the compressor at pressure p3 & Temperature t4. Necessity of Multi-stage Compression We know, sometimes we required air at high pressure. In this case if we use single stage compression for producing high pressure air then it shows following drawbacks. 1) The size of cylinder should be too large. 2) Due to compression there is rise in temperature of air, so it is difficult to reject heat from air in small time available during compression. 3) At the end of compression temperature of air is too high. It may heat-up the cylinder head (or) burn the lubricating oil. 4) So, to overcome above difficulties two (or) more than two cylinders are provided in series with inter cooling arrangement between them.  Benefits of Multi-stage Compression Improved efficiency. Two-stage compressors perform less work to compress air to a given pressure, which means your operating costs are lower. Better reliability. The intercooling stage of two-stage compression creates less chance of overheating, which in turn means more uptime and better productivity. Less moisture buildup. Cooler air has a lower moisture content. Moisture in compressed air can lead to equipment failure and premature wear. Using a two- or three-stage compressor can potentially save you from having to purchase a separate air dryer. Smaller footprint. For heavy-duty applications, multi-stage compressors deliver greater air pressure (PSI) at higher capacities (CFM) than single-stage machines of a comparable size. Few maintenance requirements. Thanks to smaller components and cooler temperatures, wearable components don’t wear out as quickly. As a result, recommended service intervals are longer.  Advantages of Multistage Compressor 1) Good energy efficiency and less power consumption. 2) It improves volumetric efficiency. 3) High Discharge pressure 4) Low operating cost. 5) Work required per Kg. of air is reduced. 6) Size of two cylinders may be adjusted to suit volume and pressure of air. 7) Small size 8) Greater Reliability 9) It gives uniform torque so smaller size of flywheel is required. 10) It provides effective lubrication due to lower temperature range. 11) Reduces power required to drive the compressor. 12) It reduces cost of compressor. 13) Lesser vibration and less maintenance. 14) It reduces leakage losses considerably. Rotary Air Compressor Rotary air compressor is a positive displacement air compressor, produced compressed air by rotary movement of blade or rotary movement of eccentric roller connected to motor. The compressor involves rotary element developing a liquid seal. This create suction at inlet and air is displaced positively by mechanical components. 1. Screw air compressor 2. Vane air compressor 3. Lobe/Root air compressor Advantages and disadvantages of rotary compressor Advantages Disadvantages 1) Rotary compressor is compact and light. 1) Discharge pressure 2) It does not exhibit vibration and shaking forces as that of the per stage is low reciprocating compressor. So it does not require a rigorous foundation. compared to the reciprocating 3) High volumetric efficiency since the clearance volume for a rotary compressor. compressor is negligible. 2) No flexibility in 4) It operates at high speed, so it can handle a large quantity of fluid. capacity and 5) Machine parts are well balanced. Less noisy. compression ratio. 6) Maintenance of low. 7) Lubrication is simple, and the output fluid is free from dirt/ oil. 8) Unlike the reciprocating compressor which discharges intermittent, the rotary compressor supply compressed air continuously 9) Low initial cost. Screw Compressor A screw compressor is a type of rotary compressor which compresses air due to screw action. The main advantage of using this compressor is that it can supply compresses air continuously with minimum fluctuation in delivery pressure. It is usually applied for low-pressure applications up to 8 bars.  Screw Compressor https://www.compair.com/en-in/technologies/screw-compressor#:~:text=An%20opening%20valve% 20sucks%20gas,the%20air%20down%20the%20chamber. Construction of screw Compressor : It is a positive displacement compressor in which compression is accomplished by the enmeshing of two mating helically grooved rotors suitably housed in a cylinder equipped with inlet and discharge ports as shown in Fig. Within the compressor, there is a set of male and female rotors. They will be designed differently so that, when turned in unison, air will become trapped between them. The male rotor (driving rotor) and consists of a series of convex lobes along the length of the rotor. Thee female rotor has concave cavities; in this way, they can mesh together without touching(very small clearance between them) to achieve compression. The entrapped gas is progressively compressed as it moves through the narrowing passage ways formed by the lobes. The inlet and outlet flow from the compressor are neither radial as in the case of roots blower nor axial but oblique. The casing is made of high grade cast iron and is ribbed for extra strength. Rotors are forged from normal carbon steel and must dynamically balance after machining. Sleeve bearings are used as shaft seals within the compressor. Unlike piston compressors which use the same principle of compression, the screw element is not equipped with valves. As such, it can work at a high shaft speed and there are no mechanical or volumetric losses to create imbalance. Working screw Compressor: In a screw compressor one of the shafts is driving shaft and the other is driven shaft. The driving shaft is connected to the driven shaft via timing gears which help to match speeds of both the shafts. The driving shaft is powered by an electric motor generally. The two shafts are enclosed in an airtight casing. The working cycle of the screw compressor has three distinct phases as following: (i) Suction process (ii) Compression process (iii) Discharge process (i) Suction process: As the rotors rotate, air is drawn through the inlet opening to fill the space between the male lobe and the female flute. As the rotor continues to rotate, the air is moved past the suction port and sealed in the interlobe space. (ii) Compression process: As the main rotor turns, the air trapped in the ineterlobe space is moved both axially and radially. The air is compressed by direct volume reduction as the enmeshing of the lobes progressively reduced the flute volume and compression occurs. (iii) Discharge process: At a fixed point where the leading edge of the flute and the edge of the discharge port co-inside, compression ceases and the air is discharged into the delivery line, until the flute volume has been reduced to zero. Advantages screw Compressor Like reciprocating compressors, it has no surging problems. It has small pipe dimensions and positive pressures due to the use of high-pressure refrigerants. it has high compression efficiency, continuous capacity control, unloaded starting, and no balancing problems. Also, the compressor is suitable for large capacity installations. Low maintenance cost Not usually noisy. Can run fully loaded for extended periods of time Good for great recovery for space heating Good efficiency for oil-flooded model Vane Compressor The operating principle for vane compressors is similar to many compressed air expansion motors. Vanes are usually made of special cast alloys, and most of the compressors are oil-lubricated. A rotor with radials, movable blade-shaped vanes is mounted eccentrically in a stator housing. When it rotates, the van is pressed against the stator walls by centrifugal force. the air is drawn as the distance between the rotor and the stator increases. The air is captured separately in the compressor pocket, which decreases in volume with rotation. The air is discharged when the vans pass through the outlet. https://youtu.be/L30JpM8Lv_A?si=i5MnvygrAp8xrqzf Construction of Vane Compressor: The Vane compressor consists of a cylindrical rotor, which is placed in the casing. This consists of intake and distribution openings, also known as inlet and outlet ports. The inlet port of the casing is larger than the outlet port of the casing. there is a drum in the centre of the rotor. It rotates eccentrically with respect to the drum casing. The vanes divide the space between the rotor and casing into a number of compartments. These vans are made of steel or synthetic fibrous material Two consecutive vanes form one compartment and due to the eccentric motion of the rotor the volume of each compartment keeps on changing. The spaces between adjacent vans create pockets of decreasing volume from a fixed inlet port to a fixed discharge port.  When the vanes reach a position where the distance between the rotor drum and the casing is short, the vane is compressed to maintain contact with the spring casing. As spring compresses, the space between the two adjacents vans also decreases. Likewise, when the vanes reach a position where the distance between the rotor drum and the casing is large, the vanes expand to maintain contact with the van spring casing. As the spring expands, the space between two adjacent vans also increases. Working of Vane Compressor: When the rotor rotates, the vane of the rotor moves outward by the casing due to the centrifugal force experienced by them until they touch the casings. When the vans move down towards inlet ports, the space between the rotor drum and the casing increases, also creating a vacuum. Thus the gas is drawn from the suction opening near the inlet of the vane compressor. After that, as the rotor continues to rotate, the compression of the trapped gas results in a decrease in the space between adjacent vans. As the space between the vans decreases, the gas volume decreases, and the gas becomes compressed. After that, the high-pressure gas that is compressed is discharged from the outlet of the vane compressor. Lobe/Root air Compressor Twin blade Tri blade Construction and Working There are two rotors in the compressor, and generally one of them is connected to the external drive that drives the other rotor. The shape, technically known as the lobe. The rotary-lobe compressor incorporates two intermeshing rotors mounted on parallel shafts. In a twin-lobe compressor, each rotor has two lobes (four lobes per compressor). In a tri-lobe machine each rotor has three lobes (six lobes per compressor). The two rotors rotate in opposite directions. As each rotor passes the blower inlet, it traps a definite volume of gas (the ‘displaced volume’) and carries it around the rotor housing to the blower outlet. With constant speed operation, the displaced volume remains approximately the same at different inlet temperatures, inlet pressures and discharge pressures. As each rotor passes the blower outlet the gas is compressed to the system pressure there and expelled. Small but definite clearances allow operation without lubrication being required inside the air casing. https://roots-blowers.com/rotary-type-positive-displacement-compressors/#:~:text=Principles%20of%20Operation,(six%20lobes%20per%20compressor).  One of the rotors is driven by the motor and the other is geared to the driven one. When one spins, the other spins in the opposite direction with very precise timing and clearances. Air is sucked into the inlet, and it is forced around by the lobes, and then pushed out of the discharge. A very small amount can escape back through the clearance in the rotors, and this is called the “slip.” When the air is discharged out of the compressor, this is when the volume reduction occurs. The air gets forced down the pipe. Unlike the other positive displacement pumps we’ve covered, that take a fixed amount of air and gradually reduce its volume to increase pressure, the rotary lobe pumps takes a fixed volume and continually forces more air into it to increase pressure. Advantages: 1. Can produce a very high volume of air. 2. Very little maintenance 3. Durable 4. Simple in design Limitations: 1. Limited pressure range. They can only give you about 15 psi. 2. They’re not always the most energy efficient, due to the slip.  Comparison Reciprocating vs Rotary air compressor Inert Gas An inert gas is a gas that does not readily undergo chemical reactions with other chemical substances and therefore does not readily form chemical compounds. Inert gases are gases which are chemically inactive, so will not undergo chemical reactions with many materials. Nitrogen Argon CO2 (in some application) Uses of Inert gas Prevention of explosive atmosphere formation in apparatus such as reactors Safe startup and shutdown of plants and apparatus Avoidance of explosion risks in storage and transport of combustible substances Protection of products against atmospheric oxygen when oxidation reactions would impair quality Protection against atmospheric moisture, either to maintain product quality or to ensure optimal downstream processing (as for example in grinding) Prevention of safety and health hazards during maintenance of equipment, apparatus and piping Purging Tank Blanketting Inerting  Continuous applications: → Blanketing of production processes to prevent fire and explosion and avoid oxidation (to safeguard quality) → Inerting of solvent containers and transport equipment to prevent fire and explosion Intermittent applications: → Purging of pipelines → Purging of tanks → Inerting of filtering installations → Inerting of silo installations → Inerting of grinding plants → Extinguishing of smouldering fires in silos Nitrogen as an inert gas Properties: Nitrogen is an inert gas that is suitable for a wide range of applications, covering various aspects of chemical manufacturing, processing, handling, and shipping. Nitrogen is a colorless, odorless, and tasteless gas. It is slightly lighter than air. It is a non poisonous gas. t is non-combustible gas and doesn't it support burning. Non Flammable t is chemically inert under ordinary conditions. Boiling point at 1 bar= –195.8 °C Melting point at 1 bar= –209.9 °C Uses of nitrogen Nitrogen is not reactive and it is excellent for blanketing and is often used as purging gas. It can be used to remove contaminants from process streams through methods such as stripping and sparging. For Inerting the headspace in process tanks or other chemical loadings. Inerting of Volatile Industrial Environments and Elimination of Volatile Organic Compounds (VOCs). Highly explosive chemical plants can be made safer by using nitrogen gas to displace oxygen from process equipment. Due to its properties it can be used for protection of valuable products against harmful contaminants. It also enables safe storage, usage of flammable compounds and can help prevent combustible dust explosions.  Nitrogen is used an inert gas to push liquids though lines, to clear lines and to propel "pigs" through pipelines to sweep out one material before using the line to transport another material. Rubber and Plastics Industry : nitrogen is used in casting Food industry: Nitrogen gas provides an unreactive atmosphere. Therefore, it can help preserve foods. to extend the shelf life of packaged foods by preventing oxidation, mold, insect infestation and moisture migration. Lighting industry: Tungsten is a metal that combusts in the presence of oxygen; this is the main reason a non-reactive gas such as nitrogen is used inside bulbs. Nitrogen is also cheaper when compared to other inert gases like argon, helium, or radon. Steel manufacturing and metal manufacturing Health Care Uses:Nitrogen is used as a shield gas in the packing of some medicines to prevent degradation by oxidation or moisture adsorption. Inerting of Volatile Industrial Environments The non-reactive nature of gaseous nitrogen makes it ideal for use in industrial environments with a high risk of spontaneous combustion. Highly explosive chemical plants can be made safer by using nitrogen gas to displace oxygen from process equipment. Other Nitrogen Gas Product Applications Gas and oil inerting systems Enhanced oil recovery Offshore inerting systems Hydrogen gas purification Industrial gas purging and blanketing Natural gas dehydration Argon Properties Argon is a colourless, odourless gas that is inert to other substances. It is nontoxic gas. Non combustible and Non flammable gas. Argon's normal boiling point is -185.9°C Argon's freezing point is –199.3°C. The gas is approximately 1.4 times as heavy as air and is slightly soluble in water. Uses of Argon Argon is the most abundant, and truly inert gas. It is used where a completely non-reactive gas is needed. Steel and metal manufacturing Argon is used as a blowing gas during manufacture of higher quality steels to avoid the formation of nitrides. also used as a shield gas in casting Argon is used as an inert gas in the manufacture of titanium to avoid oxidation and reaction with nitrogen Argon is used in the manufacture of zirconium. Lighting Industry: Argon is used as a filler gas in fluorescent and incandescent light bulbs. This excludes oxygen and other reactive gases and reduces the evaporation rate (sublimation rate) of the tungsten filament, thereby permitting higher filament temperature. Most common of the mixtures is 93% argon and 7% nitrogen. Argon is used in fluorescent tubes and low-energy light bulbs. A low-energy light bulb often contains argon gas and mercury. When it is switched on an electric discharge passes through the gas, generating UV light. The coating on the inside surface of the bulb is activated by the UV light and it glows brightly. Food and Beverages Uses: Argon is used to displace oxygen in barrels and thus prevent decomposition of foods.. Health Care Uses: Argon is used to perform precise cryosurgery, which is the use of extreme cold, to selectively destroy small areas of diseased or abnormal tissue, in particular on the skin. Other uses: Double-glazed windows use argon to fill the space between the panes. The tyres of luxury cars can contain argon to protect the rubber and reduce road noise. Pure argon, and argon mixed with various other gases, is used as a shield gas in TIG welding ("tungsten inert gas“) Plasma-arc cutting and plasma-arc welding employ plasma gas (argon and hydrogen) to provide a very high temperature when used with a special torch.