Compressor

Asep Handaya Saputra

Dept. Teknik Kimia - FTUI

sasep@che.ui.ac.id

Classification

Positive Displacement: this type of compressor includes reciprocating rotary screw, sliding vane. liquid ring and rotary lobe. The compression principle is volumetric displacement – reducing the gas volume increase pressure.

Kinetic or Dynamic: this type of compressor includes centrifugal and axial compressors. The compression principle is acceleration and deceleration of the gas - kinetic energy is converted into pressurize.

Reciprocating Integral Frame Balance Opposed Frame

Turbo Compressor Axial compressor Centrifugal Compressor

Rotary Compressor Screw Two Lobe Sliding Vane Liquid-Piston

Compressor Types

Centrifugal Compressor

Selection Guideline

Selection Guideline - Driver

Low speed can be considered anything less than about 500-600 rpm

Application Range

COMPRESSOR POWER REQUIREMENTS

The theoretical amount of energy needed to compress a given amount of a gas between specified suction and discharge conditions is independent of the compressor unit.

The actual amount of energy used depends on the efficiency of the compressor and its driver

Basic Thermodynamic Eq’n

The process is reversible S=0 and Adiabatic Process Q=0

E = Overall Efficiency (mechanical eff and polytrophic Eff.)

Theoretical Power

Line AB is for an isentropic compression. With a reciprocating compressor it will be one stage; with a centrifugal it can be one stage or that number of stages in series before gas cooling is required.

Line BC is a gas cooling step. Line CD represents a subsequent stage or stages, if any

This Figure can be used to find an approximate hisen in a manual calculation for a 0.65-0.75 relative density hydrocarbon gas.

This figure also can beused to estimate the outlet temperature for a specified set of conditions.

General Equation

Overall Efficiency = (Isentropic or Polytrophic Efficiency) (Mechanical Efficiency)

Mechanical Efficiency Bearing, Seal, Gearbox, etc.

Simple Correlation to Estimate Power

Calculation of Power

Adiabatic Compression:

PVk = Constant k = Cp/Cv

Value of k

Power per Stage

For centrifugal Compressors a value of E, 0.65 to 0.80 is suitableFor reciprocating compressors use 0.7 to 0.75 for high speed units and 0.83 to 0.90 for low speed

Simpler Power Calculation

Efficiency Isentropic vs Polytropic

Both approaches produce the same basic result. Process engineers tend to favor the isentropic method while compressor specialists favor polytropic.

Impeller

Casing of Centrifugal Compressor

Seal

Seal

Two Stages Reciproc-Compressor

Calculation

Calculation

Their primary applications are in air compression, refrigeration service, fuel gas compression, and low to medium pressure gas boosting service.

They offer positive displacement characteristics without the vibration and unbalanced forces associated with reciprocating machines.

They are manufactured in two configurations-dry (or oil-free) screw and oil flooded screw.

ROTARY SCREW COMPRESSORS