Comparative study of reciprocating and Rotary compressor project report

INTRODUCTION OF 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. 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.

Working Principle

In reciprocating air compressor, as the piston moves towards the BDC, the air is sucked into the cylinder from the atmosphere and when it moves  towards the TDC, the compression of the air starts and keeps on going and pressure increases. When the pressure increases upto its design limit it pushes the discharge valve to open and the compressed air is delivered to the storage tank.

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

WORKING

The reciprocating compressor is either powered by electric motor, diesel/gas engines.

As power is On, the electric motor starts rotating and also rotates the crankshaft attached to it. The piston starts doing to and fro motion inside the cylinder.

As the piston moves downward (towards BDC), the air from the atmosphere enters into the chamber of the cylinder.

Now the piston after reaching at BDC, starts moving upward (i.e. towards TDC), the compression of the air starts and its pressure begins to increase.

When the pressure inside the cylinder increases above the pressure of the discharge valve, the discharge valve opens and the compressed air is delivered to a air storage tank from where it is utilized for the work.

Types of Reciprocating Air Compressor

Single Acting

Double Acting

Single stage air Compressor

Double stage  air Compressor

1. Single Acting

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.

2. Double Acting

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.

3. Single Stage

In single stage reciprocating air compressor the compression of the air takes place in a single cylinder. In the first stroke, it sucks the air from the atmosphere and in the second stroke it compresses it and deliver it to the storage tank.

4. Double Stage Reciprocating Air Compressor

In this types of compressor, the compression of the air takes place in two stages i.e. the air is first compressed to some extent in one cylinder and than it is transferred to the second cylinder for further compression. Finally the compressed air is stored in a tank.

 Advantages and disadvantages of reciprocating compressor

 Advantages

• Used to produce high-pressure gas.
• It can compress gases and refrigerant of a wide range of molecular density.
• High efficiency and flexibility.
• Cheap and rugged design.

Disadvantages

1. One of the drawbacks of the reciprocating compressor is that it cannot self-regulate its capacity against a given output pressure, it will continue displacing the gas until told not to do.
2. The size of compressor is very large for a given capacity.
3. Part of the work input is lost due to frictional resistance between the piston and cylinder.
4. Pulsating of fluid flow. The operation can be made smooth by using a flywheel.
5. High vibration and noise.
6. Piston rings and valves are extremely sensitive to the dirt present in the fluid.

Applications

1. IHI Reciprocating compressors comply with API 618 and are capable of handling all kinds of process gases for the following application.
2. 
   
3. Cryogenic & other Low-temperature gases:
4. 
   
5. LNG (Liquefied Natural Gas) Boil-off gas handling at LNG Terminals
6. LPG (Liquefied Petroleum Gas) Boil-off gas handling
7. LEG (Liquefied Ethylene Gas) Boil-off gas handling
8. Ammonia Boil-off gas handling, etc.
9. Petrochemical & chemical gases:
10. Ethylene
11. Propylene
12. Butane / Propane
13. Organic Gases, etc.
14. Refining process gases & Natural gas processing:
15. Hydrogen
16. Hydrocarbon gases
17. Nitrogen
18. Methane, etc.

B) ROTARY COMPRESSOR (Construction and Working)

Rotary compressor is the type of positive displacement compressor. As the name suggests, rotary compressor produces compressed fluid/ refrigerant by the rotary movements of blades or the movement of eccentric roller connected to the motor shaft. Since the clearance volume for a rotary compressor is negligible, its volumetric efficiency is high compared to the reciprocating compressor. Normally the prime mover (motor) and the compressor is pressed into a single cylinder with no vapor space between compressor and shell. So they are also small and light. One of the most important features of the rotary compressor is that it lacks the suction and discharge valves as used on the reciprocating compressor.

*The dynamic action compressor like a centrifugal compressor and axial compressor are also categorized as a rotary compressor in some instance.

*Difference between reciprocating compressor rotary compressor

The general construction of the rotary compressor has a cylinder with an intake and discharge port, and it has a roller inside the cylinder. The roller rub against the inside wall of the cylinder while it rotates. The fluid (refrigerant) is get trapped between the space between rotor and cylinder. The trapped fluid is then progressively get compressed by decreasing the annular space between the rotor and cylinder. The process can be described in four intermediate steps.

1. Introduction of fluid into the compartment between roller and cylinder.

2. Sealing the suction port and trapping the fluid inside the chamber.

3. Compression of fluid by decreasing the volume of the chamber.

4. Discharging of high-pressure fluid through the discharge port. 

Types of Rotary Compressor

1)Root Blower

Fluid is trapped in pocket surrounding the lobes and carriedout from the intake side to exhaust. Root blower are also used in reverse to measure the flow of gases or liquids, for example in gas meter                                                 Applications: induction device on two stroke diesel engine

2)Vane type compressor

As the rotor rotates , the disc also rotates ,thus allowing sliding plates to slide as the inner surface of the casing in accentric.thus the sliding plates moves away from the centre , huge quantity of air will be trapped in, thus thus as the plate converge ,the air get compressed and thus result in compressed air.

 3)Screw Compressor

Two screw rotate with each other ,thus trapping air between the screw and the compressor casing , forming pocket which progressively travel and get squeezed and delivering it at a higher pressure which opens thhe delivery vave.

4)Scroll compressor

The scroll outer edge trap air and then as they rotate, the air travel from outwards to inwards thus getting compressed due to the reduction in the area.

Thus the compressed air is delivered through the central space of the scroll to the delivery air line.

Advantages Screw Compressors Compared to Piston Compressors:

1. Screw compressors have 25 to 30 percent higher energy efficiency than piston compressors.

2. Screw compressors have a lot less noise and vibration than piston compressors.

3. Screw compressors occupy less space than piston compressors.

4. In screw compressors, portable parts have been used a little and most of the components are static and the oil plays an important role in the air carrier, so it is very low in scroung devices. Reverse in piston compressors due to the number of moving parts, including rims - crankshaft, shaftron, piston, valves, propeller, etc., as well as inertia in returning compressors, in addition to shaking and creating high energy loss and high wear and tear And wear will be in pieces.

5. In the screw compressors, in order to install the load / unload system, the compressor does not stop completely when the pressure of the reservoir reaches the desired pressure, and when the automatic pressure is lowered out of the idling state and the air produces Therefore, a lower-capacity reservoir can be used. In the   case of piston compressors with a systeem on / off, the high capacity of the reservoirs should be used in order to prevent the compressor off and on, which results in electricity costs and depreciation, which subsequently requires The cost is high.

6. Screw compressors in excess of 2000 liters per minute have a lower maintenance load than piston compressors.

7. Several sets of screw compressors can be connected to the grid through a grid, and the energy and energy optimization policy is applied.

8. In the screw compressors, the control of the air-conditioning process - the installation of the inverter as well as the state of the device is very complete and simple.

9. In the screw compressors, due to fan and radiator cooling oil and air, the compressor can continue without stopping hours.

10. In the screw compressors due to the independent cooling fan and the coolant system, the outlet air is far cooler than the piston compressors and is prone to humidification.

Disadvantages of Screw Compressors Compared to Pistons:

1. Screw compressors are more expensive than piston compressors.

2. Screw compressors with a capacity of less than 2000 liters per minute have more maintenance than piston compressors.

3. In capacities below 500 liters per minute, piston compressors also have high competitive advantages, which can be referred to as the initial cost - low maintenance costs - the simplicity of the system.

4. Failure to observe maintenance - Use of inappropriate oil and non-standard parts of the device will be vulnerable.

5. The wheel requires a more experienced operator to maintain the machine.

Applications

Rotary-screw compressors are generally used to supply compressed air for larger industrial applications. They are best applied in applications that have a continuous air demand such as food packaging plants and automated manufacturing systems. In larger facilities, that may have only intermittent applications, the average usage among the many work stations will place a continuous demand on the compressor. In addition to fixed units, rotary-screw compressors are commonly mounted on tow-behind trailers and powered with small diesel engines. These portable compression systems are typically referred to as construction compressors. Construction compressors are used to provide compressed air to jack hammers, riveting tools, pneumatic pumps, sand blasting operations and industrial paint systems. They are commonly seen at construction sites and on duty with road repair crews throughout the world.

Conclusion

I hereby conclude that the project assigned to my for this semester was very creative and important topic of the syllabus which helped us to gain more information about the topic . the “ Study of rotary and reciprocating compressor ”  is very intrested in Mechanical field and its used are world  wide 

References

1. Power engineering  (Author is R.K khanna)
2. https://www.brighthubengineering.com/hvac/64884-different-types-of-air-compressors/
3. http://www.compressed-air-parts.com/advantages-and-disadvantages-of-air-compressor-types
4. 4.https://en.m.wikipedia.org › wikiWeb resultsReciprocating compressor - Wikipedia