CENTRIFUGAL COMPRESSOR

CHOKE LIMIT: Choke flow is the high flow limit of any type of dynamic compressor curve that caused by high velocity friction. In other words, choke or stonewall is defined as the maximum flow given impeller can handle. This value will be attained when the ratio of the relative inlet gas velocity to the sonic velocity of the gas being handle is equal to 1.0. The cause of this phenomenon is excessive relative gas velocity through the impeller; as the head (energy) required by the process system is reduced, the volume flow through the impeller will increase.

Turndown: The percentage of change in capacity (referred to rated capacity) between the rated capacity and the surge point capacity at the rated head when the unit is operating at rated suction temperature and gas composition.

Operating stability: The operating range from the compressor rated point to surge at constant speed expressed as a percentage.

Compressor Rated point : The intersection on the 100% speed curve corresponding to the highest capacity of any specified operating point.

Stability analysis: The determination of the natural frequencies and the corresponding logarithmic decrements of the rotor/support system using a complex Eigen value analysis.

Stall: The volume flow capacity below which an axial compressor becomes aerodynamically unstable. This is caused by blade drag due to non-optimum incidence angles.

Settling out pressure: The pressure of the compressor system when the compressor is shut down.

Surge: The volume flow capacity below which a centrifugal compressor becomes aerodynamically unstable.

Pinion(s): The high-speed rotor(s) in a gearbox.

Modular rotor: A rotor which is built up using stub shafts or similar devices, and held together by one or more through bolts (see Annex 2C).

Integrally geared compressors: are used mainly in petrochemical applications characterized by low flow and high pressure, or high flow and low pressure. Features & Benefits High efficiency and operating range Very high reliabilityHydrodynamic bearings: Bearings that use the principles of hydrodynamic lubrication. The bearing surfaces are oriented so that relative motion forms an oil wedge, or wedges, to support the load without shaft-to-bearing contact.

Axial flow compressors : are mainly used for applications where the head required is low and with the high intake volume of flow. The efficiency in an axial flow compressor is higher than the centrifugal compressor

Reciprocating Compressors : They are used mainly when high-pressure head is required at a low flow.

Centrifugal Compressors : Centrifugal Compressors are suitable for large flow rate.

API 617 7th edition :

CONTENTS :

Chapter 1 - General requirements

Chapter 2 - Centrifugal and axial compressors

Chapter 3 - Integrally geared compressors

Chapter 4 - Expander-compressors

CENTRIFUGAL PUMP

Pump : Hydraulic machine which converts mechanical energy into hydraulic energy (normally pressure energy).

Shut off head: Differential head developed by pump at zero flow.

End of curve: Maximum flow that a pump can deliver.

End of curve value is required to determine motor rating for parallel operation or when pump is required to be started with discharge valve open.

Cavitations: Formation and subsequent collapse of vapor bubbles in liquid due to dynamic action.

Barrier fluid: fluid, at a higher pressure than the process pressure being sealed, introduced between pressurized dual (double) mechanical seals to completely isolate the pump process liquid from the environment

Buffer fluid: fluid, at a lower pressure than the process pressure being sealed, used as a lubricant or buffer between unpressurized dual (tandem) mechanical seals

Best efficiency point BEP: flow rate at which a pump achieves its highest efficiency

Dry critical speed: rotor critical speed calculated assuming that there are no liquid effects, that the rotor is supported only at its bearings and that the bearings are of infinite stiffness

Wet critical speed: rotor critical speed calculated considering the additional support and damping produced by the action of the pumped liquid within internal running clearances at the operating conditions and allowing for flexibility and damping within the bearings

Net positive suction head NPSH:Total absolute suction pressure determined at the suction nozzle and referred to the datum elevation, minus the vapour pressure of the liquid

Oil mist lubrication: Lubrication provided by oil mist produced by atomisation in a central unit and transported to the bearing housing, or housings, by compressed air

Pure oil mist lubrication:Dry sump systems in which the mist both lubricates the bearing(s) and purges the housing and there is no oil level in the sump

Purge oil mist lubrication:wet sump systems in which the mist only purges the bearing housing

Pumps in Serial - Heads AddedWhen two (or more) pumps are arranged in serial, their resulting pump performance curve is obtained by adding theirheads at same flow rate as indicated in the figure below.

Centrifugal pump in series are used to overcome larger system head loss than one pump can handle alone. For two identical pumps in series the head will be twice the head of a single pump at the same flow rate. With constant flow rate the combined head moves from 1 to 2. In practice the combined head and flow rated moved along the system curve to 3.If one of the pumps stops, the operation point moves along the system resistance curve from point 1 to point 2 - head and flow rate are decreased.Series operation of single stage pumps is seldom encountered - more often multistage centrifugal pumps are used.

Pumps in Parallel - Flow Rate AddedWhen two or more pumps are arranged in parallel their resulting performance curve is obtained by adding their flow rates at the same headas indicated in the figure below.

Centrifugal pumps in parallel are used to overcome larger volume flows than one pump can handle alone. Fortwo identical pumps in parallel the flow rate will double (moving from 1 to 2) compared to a single pump if head is kept constant. In practice the combined head and volume flow moves along the system curve as indicated from 1 to 3.If one of the pumps in parallel or series stops, the operation point moves along the system resistance curve from point 3 to point 1 - the head and flow rate are decreased. Pumps : A pump is a machine for raising a liquid - a relatively incompressible fluid - to a higher level of pressure or head.

Compressors : A compressor is a machine for raising a gas - a compressible fluid - to a higher level of pressure.

Blowers : A blower is a machine for moving volumes of a gas with moderate increase of pressure.

Fans : A fan moves large amounts of gas with low increase in pressure.

NPSHA : NPSH determined by the purchaser for the pumping system with the liquid at the rated flow and normal pumping temperature

NPSHR : NPSH that results in a 3 % loss of head (first stage head in a multistage pump) determined by the vendor by testing with water

Normal operating point : point at which the pump is expected to operate under normal process conditions

Rated operating point : point at which the vendor certifies that pump performance is within the tolerances stated in this International StandardPUMP OPERATING REGION: TEMA B generally for chemical process services, more stringent than TEMA C, but not as stringent as R; TEMA C for generally moderate commercial and process application requirements. Probably the most commonly used in our industry TEMA R the highest integrity design.

Steam Turbine : Efficiency = ( h1-h2 ) / ( h1-h2' )P = m ( h1-h2 ) + (m-x ) (h2-h3) Rigid shaft : Rigid shaft have their first lateral critical speed in air, above the operating speed.

Flexible shaft : Flexible" or "slender" rotors have their first lateral critical speed in air, below the operating speed.

Proximity probe: A non-contacting sensor that consists of a tip, a probe body, an integral coaxial cable, and a connector and is used to translate distance (gap) to voltage.

Peak-to-Peak value (pp): The difference between positive and negative extreme values of an electronic signal or dynamic motion.

Accelerometer: - Transducer whose output is directly proportional to acceleration. Most commonly use piezoelectric crystals to produce output.

Keyphasor - A signal used in rotating machinery measurements, generated by a transducer observing a once-per-revolution event.The keyphasor signal is used in phase measurements for analysis and balancing. (Keyphasor is a Bently Nevada trade name.)

The keyphasor is an electric pulse, or trigger, which is derived from a point on a rotating shaft. It serves as a zero phase reference for determining where imbalance is on a rotor.

GAS LAW :

Boyle's law shows that, at constant temperatureAs a mathematical equation, Boyle's law is:

Charles's Law shows that, at constant pressure

Gay-Lussac's law

Standard cubic feet per minute (scfm)Million standard cubic feet per day (mmscfd)

Specific speed : index relating flow, total head and rotational speed for pumps of similar geometry

suction-specific speed : index relating flow, NPSHR and rotative speed for pumps of similar geometry

API 611 API 612

Built up rotor Solid rotor

Sleeve journal bearings Tilt pad journal bearings

Carbon ring steam seals Laby steam seals

Keyed shaft Integral coupling hub

NEMA D governor NEMA D governor

Turbines shall be given a 1-hour Turbines shall be given a 4-hour Uninterrupted no-load running test uninterrupted no-load running test

at maximum continuous speed. at maximum continuous speed

API 617 API 672

Petroleum, Chemical and Gas Air compressor Petroleum, Chemical and Gas Industry Services Industry Services

STEPS TO COMPRESSOR SELECTION & SIZINGI Understand the Application What is the compressor supposed to do?II Find Out the Details Gas, pressures, temperatures, capacities, etc.?III Scope of Supply Who is to supply the motor, switchgear, piping, etc.?IV Size the Compressor V Select Accessories

Dry Bulb Temperature : The Dry Bulb Temperature refers basically to the ambient air temperature. It is called "Dry Bulb" because the air temperature is indicated by a thermometer not affected by the moisture of the air. Wet Bulb temperature : The Wet Bulb temperature is the temperature of adiabatic saturation. Dew Point : The Dew Point is the temperature at which water vapor starts to condense out of the air

Cooling Tower EfficiencyThe cooling tower efficiency can be expressed as = (ti - to) 100 / (ti - twb) (1)where = cooling tower efficiency - common range between 70 - 75%ti = inlet temperature of water to the tower (oC, oF)to = outlet temperature of water from the tower (oC, oF)twb = wet bulb temperature of air (oC, oF)The temperature difference between inlet and outlet water (ti - to) is normally in the range 10 - 15 oF.