6.COMPRESSOR.ppt

COMPRESSOR

PAB 2053

Outline

Introduction Reciprocating compressor Rotary compressor Centrifugal compressor Planned Preventive Maintenance

Introduction

Compressors are used to flow gas from lower pressure to higher pressure system

Gas lift, gas injection, gas storage, sales gas (evacuation and distribution), NGL recovery, LNG etc.

Many types of compressors but only few are commonly used in oil and gas field

Compressors receive their source of energy from drivers or prime movers

Suction scrubber is very important – absolutely necessary to prevent contaminants/dirt/salt (solids and liquids) from entering compressor

Discharge Pressure – outlet Suction Pressure – inlet

Types and Classification

COMPRESSOR

POSITIVE DISPLACEMENT

KINETIC (DYNAMIC)

RECIPROCATING ROTARYCENTRIFUGAL (RADIAL FLOW)

AXIAL FLOW

Single-Stage

Multi-Stage

Screw

Sliding Vane

Single-Stage

Multi-Stage

Positive Displacement

Pressure of gas is increased by reducing its volume Piston or screw or vanes moves inside a cylinder Gas trapped inside the cylinder are compressed

(reduced in volume) as the components moves/rotates

The compressed gas has higher pressure

Reciprocating Compressor

Main components are piston and cylinder Reciprocating cycle has four steps: compression,

discharge, expansion and suction

Reciprocating Compressor

Reciprocating compressor

Classified as high speed (900 -1200 rpm) or low speed (200 – 600 rpm)

No. of ‘throws’ = no. of pistons Stage of compressor (compression stage)

Each stage has its own suction scrubber, cylinder and after-cooler

No. of throws not equal no. of stages Two-stage four-throw compressor two

cylinders working in parallel, sharing one suction scrubber and one after cooler (discharge)

Reciprocating compressor

Sizes – 50 hp to 3000 hp Low-speed best used when

Large horsepower increments required Very high pressures involved Heavy molecular weight gases involved Long project life Fuel efficiency is important

High-speed Horsepower increments less than 4000 hp Short project life

Low-speed

High-speed

Rotary – Screw Compressor

Helical or spiral lobe compressors Two helical rotors (one with rounded tips and one

with rounded grooves) rotated by timing gears Each groove is filled with gas and when rotors

rotate towards each other, the trapped gas is compressed

Compressed gas is then discharged at outlet port Can be oil-lubricated or non-lubricated Up to 400 hp (for oil and gas service) and

Discharge pressure up to 250 psig More efficient at low discharge pressure (<50 psig) Takes 10 – 20% more horsepower at higher

discharge pressure (>50 psig)

Screw Compressor

Vanes fitted into slots on the rotor Vanes slide in and out as rotor rotates Gas fills in between the vanes and wall of cylinder As rotor rotates, gas trapped is compressed

because volume is reduced Lubricated by oil Mostly used for application under 125 hp and

Discharge pressure usually less than 100 – 250psig Small, inexpensive for low hp service

Rotary - Sliding-Vane compressor

Sliding-Vane compressor

Kinetic Energy Compressor

Pressure is increased by reducing velocity of gas from high to low Gas enters eye of impeller and accelerated

outward the impeller as the impeller moves The acceleration imparts kinetic energy to the

gas As gas leaves the impeller, gas slows down and

expands and some kinetic energy converted to pressure energy

Centrifugal Compressor

Centrifugal compressor

Important Components

Impeller (rotating) circular blades or wheels Important because impeller imparts the kinetic

energy to gas Stationary parts

Diffusers – flow channels for gas from exit of one impeller to inlet of another impeller

Diaphragms – solid walls of the channels Casing

Houses the stationary and rotating parts Vertically split (barrel) or horizontally split

Planned Preventive Maintenance

Compressors are the most expensive gas-processing equipment to buy and operate and so good maintenance is essential

Objectives of maintenance program Ensure safety of personnel Keep equipment running reliably Minimise costs

Cost control is challenging. Planned Preventive Maintenance is the approach to provide adequate repair and monitoring services at minimum cost

PPM program

1. Regulations and codes All applicable governmental regulations must be

followed and industry codes should be considered carefully

2. Lubrication system Lubrication is to prevent wear and tear Too much lubrication and too little is bad Lube oil must be regularly checked for

contaminants

3. Monitoring and shutdown system