Brief Discussion on the Functions of Components of Skid-mounted Reciprocating Compressor Unit
Nowadays, most high-speed reciprocating compressors are assembled and complete sets in factories. They are pre-assembled to facilitate transportation and quickly establish contact with customers, greatly reducing installation time and costs...
The most common compressors in oil and gas plants are reciprocating compressors. In industrial process applications, traditional large and small skid-mounted compressors and split compressors are generally installed in the unit components, pipelines and assembly lines with the most reinforcement On a concrete foundation. Nowadays, most high-speed reciprocating compressors are assembled and complete sets in factories. They are pre-assembled to facilitate transportation and quickly establish contact with customers, greatly reducing installation time and costs.
This article will discuss the important components and functions of the reciprocating compressor unit.
Typical reciprocating compressor unit
High-speed reciprocating compressor, driven by natural gas engine or electric motor, realizes lower basic cost, shorter installation time and better compactness. It has become the most common equipment suitable for the upstream market, and it has also occupied many midstream natural gas compressor markets. The power of the unit ranges from 50hp (37kW) or less, and 5000hp (3729kW) or more. Larger units can also be made skid-mounted, but they often require on-site assembly due to their large size.
Some technical standards can be used to standardize the design and structure of reciprocating compressors. For example, the standards API IIP "Technical Specification for Skid-mounted Reciprocating Compressors for Oil and Gas Industry" and ISO 13631 "Skid-mounted Reciprocating Process Compressors for the Oil and Gas Industry" are often used to regulate the design and application of upstream process compressors. Assembly. Recently, the GMRC (Gas Machinery Research Committee) released the "Guide to High-speed Compressors for Field Gas" based on the technology of extensive industry cooperation, which provides more comprehensive guidance for the application of upstream compressor units, and the unit power reaches 2000hp (1491kW).
Standard API 618 "Reciprocating Compressor for Petroleum, Chemical, and Gas Industry Services" is used in the design and assembly of many midstream and downstream compressor applications. In 2013, GMRC's "Guidelines for High-Speed
Reciprocating Compressors for Weather Transportation and Storage" provided more technical guidance for the design and assembly of compressor units with a midstream power greater than 2000hp.
Most of the units are installed on the welded I-beam base and consist of gas engines, compressors and air-cooled heat exchangers, so that a complete skid-mounted compressor system can be realized and assembled in a factory. And it can be transported to the field by one or more trucks. This base can also be used as a platform to install other components, such as an intake filter that removes moisture from the gas, and a buffer used to relieve pressure pulsation from compressors, control panels, pipes and other devices.
There are many types and sizes of reciprocating compressors. This article only lists some of the more common ones. Figure 1 is a small air compressor in the traditional sense. It is a 215hp three-stage reciprocating compressor driven by a two-stroke gas engine with a speed of 1800rpm, which is specially used for oil production.
Brief Discussion on the Functions of Components of Skid-mounted Reciprocating Compressor Unit
Figure 2 is one of several two-stage reciprocating compressors driven by a four-stroke gas engine with a power of 1895hp and a speed of 1000rpm, which is dedicated to central gas collection. It is generally built on the basis of crushed stone or gravel. For air compressors with a power of 2000hp, they are generally assembled on this basis. Depending on the type of soil and the humidity of the environment, reinforced concrete or piling is used, and sometimes suitable supports are required. In some places where it will not freeze for a long time in winter, the unit can be operated in the open air.
Brief Discussion on the Functions of Components of Skid-mounted Reciprocating Compressor Unit
Figure 3 is a three-stage reciprocating compressor driven by a four-stroke gas engine with a power of 1380hp and a speed of 1400rpm, which is dedicated to central gas collection. Such a unit needs to be installed on a reinforced concrete foundation, and a factory shed with a closed upper part and open on both sides is required to protect the unit and maintain ventilation.
Brief Discussion on the Functions of Components of Skid-mounted Reciprocating Compressor Unit
Figure 4 is a two-stage reciprocating compressor driven by a four-stroke motor with a speed of 1200 rpm with a power of 2000 hp, which is used for supercharging a gas processing device. It needs to be installed on a reinforced concrete foundation and needs to be completely enclosed in a closed building equipped with an overhead crane to ensure that heavy components can be lifted safely. The air-cooled heat exchanger of this equipment is usually installed outside the building independently of the compressor unit.
Brief Discussion on the Functions of Components of Skid-mounted Reciprocating Compressor Unit
Figure 5 is a one-stage reciprocating compressor driven by a six-stroke gas engine with a power of 5045hp and a speed of 1000rpm for gas transmission. The whole is similar to Figure 4, it is built on a reinforced concrete foundation and needs to be completely enclosed in a closed building equipped with an overhead crane to ensure that heavy components can be lifted safely. Its air-cooled heat exchanger is almost always installed outside the building independently of the compressor.
Brief Discussion on the Functions of Components of Skid-mounted Reciprocating Compressor Unit
The main components and functions of the reciprocating compressor unit
The traditional mobile air compressor is shown in Figure 6, and the important components have been marked for reference.
The compressor unit sucks the gas on the low pressure side (indicated by the green arrow) and delivers it to the high pressure side (indicated by the red arrow). The compressor unit in this example is a two-stage (rentable) unit operating in the open air near the water source. Each of its important components will be described in detail below.
base
All components of the compressor are installed on a base made of welded I-steel. The standard base has two main rotatable beams, which can extend the length of the base to support the engine and compressor. Most bases have additional rotatable beams all around. And there are many common beams to support various components. In most cases, units of this size will be covered with a layer of reinforced concrete on the base where the engine and compressor are placed. Concrete can not only play a buffer role, but also increase the overall mass to reduce the vibration caused by the natural frequency of the machine. In actual gas applications, the base is generally built on a foundation with sufficient drainage capacity such as gravel or gravel. It supports the entire compression system whether it is under load, transportation, unloading, or operation.
compressor
It is the heart of the whole system. Figure 6 is a four-stroke two-stage compression reciprocating compressor. The compressor generally has 1 to 6 rows, and the typical design can be 1-4 stages. Take the two-stage compressor, as shown in the figure, the first stage is on the back, the second stage is on the front, and each stage has two parallel cylinders.
gas engine
The compressor in Figure 6 is driven by a sixteen-cylinder reciprocating gas engine through a flexible coupling. Gas engines can provide a range of operating speeds, usually between 75% and 100% of the rated speed. As shown in Figure 4, the motor can also be used to drive the compressor. But the working speed of the motor is constant unless a frequency converter is installed.
Brief Discussion on the Functions of Components of Skid-mounted Reciprocating Compressor Unit
Catalytic exhaust gas purifier/exhaust muffler
In Figure 6, installed on the top of the air-cooled heat exchanger is a combined catalytic exhaust gas purifier and an exhaust muffler installed on the exhaust pipe of a gas engine. During installation, sometimes the two are separate. But in most cases, in order to save space and cost, they are generally tied together and installed.
Intake throttle valve
In the actual compression application, the function of the intake throttle valve is to control the gas flow and control the working state of the compressor within a safe range. As shown in Figure 6, it is installed on the low-pressure intake pipe, which is the front end of the entire compressor system. In some cases, it is also installed on the base, just behind the low-pressure intake pipe. The intake throttle valve can reduce the gas pressure entering the compressor to achieve the purpose of reducing the mass flow. Usually this can reduce the power consumption when compressing gas, but sometimes this effect is not achieved.
Bypass valve
Another common equipment in compressor systems is the bypass valve, also called the recirculation valve. It is installed on the pipe connecting the compressor discharge port and the intake port. The function of the bypass valve is to realize the bypass of the compressor suction and exhaust. Although this cycle reduces efficiency, the connection between exhaust and intake can balance the pressure at the suction and exhaust ports of the compressor, which can effectively reduce the torque of the compressor and the power required for starting the gas engine or electric motor. At this time, the bypass valve works intermittently. When the compressor works under extreme conditions, in order to reduce the maximum working load, the bypass valve can be opened continuously, and the pipeline must be connected behind the gas cooler, as shown in Figure 6. Show.
intake filter
The front end of each air inlet of the compression system needs to install an air inlet filter. It can filter a small amount of liquid mixed in oil and gas. The intake filter consists of a liquid level indicator and a controller that can automatically clean the liquid in the filter. The first-stage filter is installed between the low-pressure pipe and the first-stage intake buffer.
Although a larger liquid separation device is installed at the front end of the compressor to separate larger water droplets, the liquid separation device of the entire system must be able to separate any liquid that may be separated from the oil and gas in order to reduce the pressure in the compressor. Pressure and temperature. This is particularly important in practical applications. Here, the moisture in the oil and gas will be saturated and mixed with hydrocarbons with a higher molecular mass. They will be affected by pressure (for example, when the gas pressure drops, passing through a valve) and temperature (for example, passing through a cold air Long pipes or air coolers) change from gas to liquid in the process of lowering. The separator can also separate the lubricating oil from the cylinder in the compressor from the branch pipe or other front-end positions.
Buffer
Because the compressor will produce high-pressure air pulsation, it will cause vibration and fatigue damage of the booster equipment. Therefore, it is necessary to use a buffer near the cylinder to smooth these pressure pulsations. The intake and exhaust ports of the compressor are generally at the top and bottom of the cylinder, so each stage of the compressor needs to install a buffer at the intake and exhaust ports. When the gas enters the cylinder from the intake filter, the buffer can eliminate the pressure pulsation from the front-end device. When the pressurized gas is discharged through the exhaust port, the buffer can eliminate the pressure pulsation from the rear device. It is a common method to design a buffer to balance all cylinders in the same stage of the compressor. For example, in Figures 2, 3, 4, and 6, the buffers in each stage are connected to two cylinders, while in Figure 5 it is connected to three cylinders.
A relatively small compressor unit, such as Figure 1, may not have a buffer in the traditional sense. But when you look closely at its gas pipeline, you will find that the diameter of its intake pipe and exhaust pipe is larger than the diameter of the pipe connecting the cylinder, so that pressure pulsation can be controlled even without using a larger pressure vessel. Generally smaller compressors use this method.
air-cooled heat exchanger
Any compressor unit needs an air-cooled heat exchanger. If the machine is set up in a field environment (not in a building), for simplicity, the air-cooled heat exchanger is always installed on the base of the unit or a dedicated base connected to the main base. However, if the machine is built in a completely enclosed building as shown in Figures 4 and 5, the air-cooled heat exchanger is usually independent of the compressor unit.
The cooler must cool the gas discharged from each stage, the coolant of the engine, the lubricating oil of the engine and the compressor, and sometimes the gas discharged from the turbocharger. These coolers allow the gas to circulate in the pipes full of fins to take away the heat of the liquid circulating in the pipes. A large fan driven by an engine or electric motor can accelerate the flow of outside air around the heat sink. If the actual application requires, the fan can also promote the circulation of gas in the pipe. There are many types of air coolers, with gas flowing in and out in parallel, and gas flowing in and out vertically.
control panel
The control panel of the system is the key equipment of the compressor system. It controls all important functions of compressor operation, including compressor start, pause, capacity control, safety alarm and shutdown functions. The control panel can be installed on the base (Figure 1, 6) or outside the base (Figure 2, 4, 5). When the control panel is installed outside the base, it can reduce the impact of vibration and high temperature generated during the operation of the unit on the control panel. At the same time, the space on the base can be overcrowded, which is convenient for maintenance.
