The centrifugal compressors supplied by Petrosadid apply the advanced technical solutions such as dry gas dynamic seals, redundant automation and control systems, vibration control and diagnostics systems and many other features to realize the following advantages:
• High reliability
• Long nonstop runs between overhauls
• Low cost of installation
• High-efficient automation and control system for operational safety including unmanned operation mode
• Energy-efficient flow path with high performance Stable operation within a wide range of variable parameters and composition of the gas being compressed
• Better serviceability due to contemporary compressor design with easy access to components for fast and simple maintenance
• Optimal price/quality ratio
• Short manufacturing and delivery lead time
Technical Data
• Capacity: up to 1,400 m3 /min (up to 120,000 Nm3 /h)
• Discharge pressure: up to 45 bar (45.8 kgf/cm2 )
• Drive power: up to 6,300 kW
• Efficiency: up to 85%
Compressible Gases
Nitrogen, Oxygen, Chlorine, Air, Associated Petroleum Gas, Fuel Gas, Hydrocarbon Process Gas, Flare Gas, Hydrogen-Bearing Gas, Coke Oven Gas
Design Features & Advantages
• Horizontally split casing in a combination with embedded parts in the flow path allow fabrication of the complex machines for compression of inflammable gases (oxygen) and gases tending to form various sediments along the flow path
• Maintenance of bearings and seals without disassembling of the casing
• Low cost of routine maintenance due to access to the rotor and embedded parts through the upper casing half
• Special design and materials requirements for compression of inflammable gases
• Many years of operation in real condition have proven high reliability and efficiency of the construction components
• Available in customized versions in accordance with customer requirements
Installation
• Version for indoor installation inside of a building (enclosure) of a compressor station
• Hangar version (prefabricated building) including all engineering systems
• Version for outdoor installation in open air areas
Compressible Gases
• Ductile cast iron
• Carbon steel
• Stainless steel
• Titanium
Drive Types
• Electric motor
• Gas turbine
• Steam turbine
Scope of Supply
• Compressor system (compressor, multiplier, base frame, couplings, piping)
• Electric motor (gas turbine drive, gas piston drive, steam turbine)Lubrication systems and seals
• Anti-surge protection system
• Automatic control system
Technical Data
• Capacity: up to 900 m3 /min (up to 220,000 Nm3 /h)
• Discharge pressure: up to 450 bar (458.8 kgf/cm2 )
• Drive power: up to 32,000 kW
• Efficiency: up to 85%
Compressible
Gases Nitrogen, Chlorine, Air, Natural Gas, Associated Petroleum Gas, Fuel Gas, Hydrocarbon Process Gas, Flare Gas, Hydrogen-Bearing Gas, Coke Oven Gas, Other Gases
Design Features & Advantages
• A vertically split casing allows fabrication of high-pressure compressors for explosive gases
• Flow path with high-performance compression stages
• Special locks securing solid forged caps that cover the ends of the steel cylinder, provide quick and easy maintenance and repair of the compressor
• Dry gas seals to provide complete purity of compressed gas and prevent its leakage into compressor room
• Active magnetic bearings for the rotor suspension
• Intercooling of compressed gas between sections in the two-stage casings
• Automation system based on microprocessor controller
• Many years of operation in real conditions have proven high reliability and efficiency of the construction components
Installation
• Version for compressor stations (placement inside the permanent building)
• Hangar version with all engineering systems (easily construction buildings)
• Block-container version with all engineering systems
• Marine version including offshore platforms
• Version for outdoor installation in open air areas
Construction Materials
• Ductile cast iron
• Carbon steel
• Stainless steel
• Titanium
Drive Types
• Electric motor
• Gas turbine
• Steam turbine
Scope of Supply
• Compression system (compressor, multiplier, base frame, couplings, piping)
• Electric motor (gas turbine drive, gas piston drive, steam turbine)
• Lubricating oil systems and seals
• Anti-surge protection system
• Automatic control system
To help understand the concepts of velocity and dynamic pressure, think about a fan that you might have in your home or office. If you place your hand in front of the fan, you can feel the kinetic energy that the fan blades have added to the air. If you place your hand behind the fan, you can feel movement of the air as it is being drawn into the fan. The suction is caused by a reduction in static pressure due to the acceleration of the air by the fan blades, thereby drawing more air into the fan.
Now imagine that you arrange several fans in a row inside an enclosure to ensure that all of the flow goes in one direction. Imagine how much force you would feel coming out of the last fan in the stack after each fan accelerates the air (i.e., adds more kinetic energy). That is the basic concept behind a compressor, a series of rotating blades adding energy to the gas.
Now suppose that the flow changes direction as it passes through the rotating blades so that it exits the blades traveling radially outward rather than in an axial direction (below figure). That is the fundamental difference between the axial compressor’s rotor and the centrifugal (or radial) compressor's impeller, the axial rotor discharges flow in the axial direction while the centrifugal impeller discharges in a radial direction.
The impeller adds kinetic energy to the fluid in the same way the blades of a household fan do, although the centrifugal impeller adds more energy to the fluid than can be added with a typical fan blade. Thus, it is possible to achieve much higher pressures with centrifugal impellers.
Centrifugal compressors have lubrication systems designed as per API 614 consisting of an oil reservoir, pumps, filter, cooler and oil lines. The programmable logic controller (PLC) starts the auxiliary AC power-driven lubricating oil pump. Pressure at the oil header creates starts the drive. If the header pressure is low, the standby oil pump starts and maintains oil pressure during operation. Oil is pumped to the lubricated parts (radial and thrust bearings). If a speed increaser gear is present, they are lubricated with the same oil as the bearings
A dry gas seal consists of a rotating, hard-face mating ring with either a machined or etched circumferential spiral groove pattern and a primary (stationary) ring in softer material. The primary ring is radially restrained but can move in the axial direction. Under static and depressurized condition, the springs behind the primary ring keep the seal faces closed and in contact. In the static and pressurized condition, the sealed gas penetrates across the faces at the tip of the groove. A sealing dam maintains uniform pressure distribution between the seal faces and helps to provide the hydrostatic lift that results in a low startup torque, lower heat generation, and less parasitic power.
In the dynamic condition, the progressively shallow spiral grooves draw the sealed gas toward the center dam and create gas film pressure to separate the faces so they become no contacting during running. Special geometry of the spiral grooves provides a uniform hydrostatic and hydrodynamic pressure distribution and maintains the proper seal face gap for gas film stiffness.
These features assist in quick liftoff, even during low-speed operation (10 fps [3.05 m/s]) for pressures less than 50 psig (345 kPa gauge) and allow the seal faces to adjust rapidly to the changes in the process conditions.
Depending on the shape of the circumferential grooves, the seals can be unidirectional (Figure 1) or bidirectional (Figure 2). A bidirectional seal provides protection from reverse rotation in situations such as the failure of dis-charge check valve and eliminates the need for spare seal cartridges on each end of a between-bearings centrifugal compressor. The spare seal cartridge can be installed at either end of the compressor. A sealing dam and land are shown in Figures 1 and 2. Figure 3 illustrates the pressure profile across dry gas seal faces during dynamic condition.
Slow speed operation of seal faces (slow roll) The rotors of between-bearings centrifugal compressors, gas turbines and steam turbines experience elastic deflection or bending during standstill condition. The external load, acting perpendicular to the axis of the rotor that results in flexure or bending of the rotor, is either due to gravity force or due to the combined effect of gravity and thermal differential across the rotor based on its operating environment.
A slow roll of the driven compressor at speeds from 2 to 500 rpm, including coast down, or ratchet slow roll at 0.125 turn per minute (typically not more than 50 rpm) to gradually relax the bow in the rotors before starting up the train requires the dry gas seals to be designed in a way that provides a face separation during slow roll and in unpressurized or pressurized conditions inside the seal chamber.
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