Oil Free Reciprocating Compressor Pdf
Wan Cabiness
A reciprocating compressor or piston compressor is a positive-displacement compressor that uses pistons driven by a crankshaft to deliver gases at high pressure.[1][2] Pressures of up to 5,000 PSIG are commonly produced by multistage reciprocating compressors.
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. Applications include railway and road vehicle air brake systems oil refineries, gas pipelines, oil and gas production drilling and well services, air and nitrogen injection, offshore platforms, chemical plants, natural gas processing plants, air conditioning, and refrigeration plants. One specialty application is the blowing of plastic bottles made of polyethylene terephthalate (PET).
In the ionic liquid piston compressor many seals and bearings were removed in the design as the ionic liquid does not mix with the gas. Service life is about 10 times longer than a regular diaphragm compressor with reduced maintenance during use, energy costs are reduced by as much as 20%. The heat exchangers that are used in a normal piston compressor are removed as the heat is removed in the cylinder itself where it is generated. Almost 100% of the energy going into the process is being used with little energy wasted as reject heat.[3]
There are two primary classifications of industrial compressors: intermittent flow (positive displacement), including reciprocating and rotary types; and continuous flow, including centrifugal and axial flow types.
Reciprocating compressors are typically used where high compression ratios (ratio of discharge to suction pressures) are required per stage without high flow rates, and the process fluid is relatively dry.
Wet gas compressors tend to be centrifugal types. High flow, low compression ratio applications are best served by axial flow compressors. Rotary types are primarily specified in compressed air applications, though other types of compressors are also found in air service.
The primary components of a typical reciprocating compressor system can be seen in Figures 1 and 2. It should be noted that the author has never seen a "typical" compressor installation, and acknowledges the existence of many exceptions.
A piston is driven in a reciprocating action to compress the gas. Arrangements may be of single-or dual-acting design. (In the dual-acting design, compression occurs on both sides of the piston during both the advancing and retreating stroke.)
Cylinders for larger applications (typical cutoff is 300 hp) are equipped with coolant passages for thermosyphon or circulating liquid coolant-type systems, whereas some smaller home and shop compressors are typically air-cooled. Large application cylinders are generally fitted with replaceable liners that are press-fitted into the bore, and may include an antirotation pin.
The distance piece (sometimes called the doghouse) is a structural member connecting the compressor frame to the cylinder. Intermixing of fluids between the cylinder and the distance piece must be avoided. Packing rings contain gas pressure within the cylinder, and they keep oil from entering the cylinder by wiping oil from the piston rod along its travel.
The running gear, housed within the compressor frame (Figure 2), consists of the crosshead and connecting rod which connect the piston rod to the crankshaft, converting its rotary motion into a reciprocating linear motion.
The crankshaft is fitted with counterweights to balance dynamic forces created by the movement of the heavy pistons. It is supported within the frame of the compressor by plain bearings at several journals. A flywheel is also provided to store rotational inertia and provide mechanical advantage for manual rotation of the assembly.
Some compressors will lubricate their frame running gear with an integral, shaft-driven oil pump, while others are provided with more extensive, skid-mounted lubrication systems. All properly designed systems will provide not only for oil circulation to the critical tribo-surfaces of the equipment, but also for lubricant temperature control, filtration and some measure of instrumentation and redundancy.
Suction gases are generally passed through suction strainers and separators to remove entrained particulates, moisture and liquid phase process fluid that could cause severe damage to the compressor valves and other critical components, and even threaten cylinder integrity with disastrous consequences.
Often the motor is manufactured to be integral to the compressor, and the motor shaft and compressor crankshaft are one-piece, eliminating the need for a coupling. Gearbox-type speed reducers are used in various installations.
An explanation of a few basic thermodynamic principles is necessary to understand the science of reciprocating compressors. Compression occurs within the cylinder as a four-part cycle that occurs with each advance and retreat of the piston (two strokes per cycle).
Note that some minimal volume remains, known as the clearance volume. It is the space remaining within the cylinder when the piston is at the most advanced position in its travel. Some minimum clearance volume is necessary to prevent piston/head contact, and the manipulation of this volume is a major compressor performance parameter. The cycle is now at point 3.
Comprehending this cycle is key to diagnosing compressor problems, and to understanding compressor efficiency, power requirements, valve operation, etc. This knowledge can be gained by trending process information and monitoring the effect these items have on the cycle.
Peter Brotherhood compressors are most commonly used in Refining and Petrochemical applications with hundreds of installations globally. Please contact us for all your service and support requirements for your Peter Brotherhood API618 Reciprocating Gas Compressor. We offer Technical Support Services, Genuine OEM Spare Parts, Training, Factory Repairs and Upgrades for your Peter Brotherhood equipment.
The first Thomassen C-85 reciprocating compressor with eight cylinders and a capacity of 16.6 MW was delivered within the challenging one-year deadline. The scale of the compression system is unprecedented. The six compressors together are responsible for compressing hydrogen for virtually all of the hydrogen suppliers and consumers within the refinery.
Universal and environmentally friendly: ECOLINE reciprocating compressors offer high cooling capacity with minimal energy requirements and are optimised for HFC, HFO and low-GWP refrigerants. The optional VARISTEP mechanical capacity control offers high part-load efficiency in medium and low temperature application.
The ECOLINE+ series is a further-developed version of the proven reciprocating compressors. By using the refrigerant CO2, innovative line-start permanent-magnet motors and optional intelligent electronics, the series achieves the highest energy efficiency values possible.
The 2-stage reciprocating compressors are designed for an extensive application range and boast an optimised drive gear and efficient motor. The highly reliable semi-hermetic series is designed to be robust and suitable for a variety of refrigerants.
Compact unit comprising efficient ECOLINE compressor and liquid receiver. The components are well coordinated and universal. These units can be used with low-GWP refrigerants, thus making them future-proof.
Compact unit comprising 2-stage semi-hermetic reciprocating compressor and liquid receiver. The components are well coordinated and universal. These units can be used with low-GWP refrigerants, thus making them future-proof.
Open drive reciprocating compressors are available in two model series: for (H)CFC/HFC refrigerants and ammonia. Due to the open drive design, standard motors can be attached to the compressor via coupling housing or belt drive. Reliability and easy maintenance have made them popular options for years.
The open drive, 2-stage reciprocating compressors are optimised for the low temperature refrigeration range. With the optional liquid subcooler, they significantly increase the cooling capacity and efficiency of the entire system. Standard motors can be attached to the compressor via coupling housing or belt drive.
A reciprocating air compressor uses piston-driven crankshafts to pressurize air and other gases, increasing their density while decreasing their volume. Air compression makes materials like natural gas easier to store, transport and use effectively.
Once the governor or pressure control device senses that the air in the receiving tank has reached the high pressure cut-out threshold, it signals the compressor to unload. Unloading may be full or partial, depending on the reciprocating compressor design.
As down-stream machinery uses the newly compressed air, the pressure level of the tank will gradually reduce. Once it falls to the pre-determined load point, the control device signals the compressor to re-start the compression cycle and build the tank pressure up once again.
One of the important reciprocating compressor basics to be aware of is the duty cycle. The duty cycle is determined by taking the time the compressor spends loaded and comparing it to the time the machine runs while completely unloaded or turned off. Reciprocating compressors are only designed for a 20% to 30% full-load time and should be unloaded the rest of the time.
Ensuring your compressor is operating within duty cycle limits is essential to maximizing its service life. Choosing an undersized compressor for your application or artificially increasing the load by ignoring air leakage will push the system beyond its capabilities and result in costly premature wear and tear in multiple components of the compressor.
Not every reciprocating compressor design works this way, but it is possible for the drive engine pump to share some of its lubrication with the compressor. In this design, the supply from the sump is essential to keeping the whole system lubricated and functioning properly.
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