Role of Compressed Air System in Textile Industries

UNIVERSITY OF KARACHI

CHEMICAL ENGINEERING

AELYA SHAH

Agenda

Introduction

Use of Compressed Air in Textile Industry

Applications

Compressed Air System  

Types of Compressor

Compressor used in Textile Industry

Optimization of Air System

Minimizing Compressed Air Cost

Introduction

Compressed air, also referred to as the "4th Utility" (after electricity, water & steam) is one of the major energy consumption utility in any industry.

Various estimates indicate that about 4,000-5,000 MW is consumed nation wide by the compressors and its related accessories & support systems.

It is a well-known fact that of the life cycle cost of any compressor, 85-90% is towards energy and only 10-15% towards initial investment & maintenance.

Hence, the design and selection of the right compressor assumes great significance while setting up your air system. It is very important on the part of each one of us using compressed air to understand a simple fact that "Air is free but compressed air is not!"

Use of Compressed Air in Textile IndustryIn Textile manufacturing units, generally following Compressed air powered pneumatic systems are used:

Spinning machine (for control purpose through valves and cylinders)

Loom Jet Weaving (for the insertion of weft).

Winding machine (for the purpose of splicing of yarn)

Use of Compressed Air in Textile Industry

Stacking Device

Printing machines

Thread Detector

Sewing Machine

Texturising

Automated Equipment

Agitating Liquids

Cleaning

Pneumatic control and actuators

System Cooling

Clamping

Blowing out residual / dust material

Sewing Needle

Conveying

Applications

Compressed Air System

The compressed air system mainly consists of:

•Supply side•Distribution &•Demand side

Compressed air systems consist of a supply side,which includes compressors and air treatment. and a demand side, which includes distribution and storage systems and end-use equipment. A properly managed supply side will result in clean, dry, stable air being delivered at the appropriate pressure in a dependable, cost-effective manner. A properly managed demand side minimizes wasted air and uses compressed air forappropriate applications.

Compressed Air System

compressed air sub system

As such the compressed air system has following six major sub systems•Air compressors•Controls•Air Quality•Storage•Distribution•Demand (consumption)

The compressed air generated by compressor is stored in the Air-receiver of sufficient capacity to smoothen fluctuations in the supply of compressed air vis-a-vis demand from individual consumption points (machines).

The air receiver helps also in cooling of air and this facilitates removal of much of the moisture in the air which is harmful for the pneumatic system.

Air-receiver

For large users/bigger compressors air dryer units are provided.

The air dryer units of two types are normally employed in the mills.

1.heatless dryer

2.refrigerated air dryer.

Air-dryer

Although, the refrigerated air dryer has higher initial cost, it has less operational cost than the heatless type. This is because in heatless dryer about 10-12% of compressed air is lost in purging thereby wasting costly electrical energy.

The air dryer helps in making the compressed air almost 100% dry – which is essential for some machines such as Air jet looms

Air-dryer

As regards air distribution network, it should be ensured that pressure drop should not be more than 0.5 kg/cm2in the longest line.

The pipe sizes are to be decided based on this consideration. Also the pipe lines should be of minimum length with less bends and fittings.

This will ensure minimum wastage of electrical power.

Air distribution

For the proper and trouble free operation of pneumatic systems provided for the machines, it is essential to ensure filteration, pressure regulation and lubrication of the compressed air.

The filteration is ensured by providing filters in the pipe line after the air receiver. These can remove dust particles upto 5 micron size.

Air filter

Pressure regulation i.e. maintaining the desired air pressure for the machines used is achieved by the use of air pressure regulator.

Pressure regulation

For reducing friction and wear and tear and preventing corrosion, proper lubrication of compressed air is necessary. This is achieved by the ‘oil-fog’ air line lubricator.

Lubrication

TYPES OF COMPRESSOR:

TYPES OF COMPRESSOR

Air compressors are mainly classified in two types based on their construction & operation:

1. Positive displacement (Reciprocating & Rotary compressors)2.Dynamic type (Centrifugal & Axial flow compressors)

Positive-Displacement Compressors In the positive-displacement type, a given quantity of air or gas is trapped in a compression chamber and the volume which it occupies is mechanically reduced, causing a corresponding rise in pressure prior to discharge. At constant speed, the air flow remains essentially constant with variations in discharge pressure.

Reciprocating compressors

It work like bicycle pumps. A piston, driven through a crankshaft and connecting rod by an electric motor, reduces the volume in the cylinder occupied by the air or gas, compressing it to a higher pressure.

Double-acting reciprocating compressors are generally water-cooled and with multi-stage versions are usually considered to be the most efficient air compressors (100 hp to 250 hp). These however, come with high initial & installation costs and higher maintenance as well.

Single-acting reciprocating compressors are generally air-cooled and available in the smaller hp sizes (1 hp to 50 hp). However, such compressors are generally less efficient than the other types.

Screw compressors

Screw compressors are available as oil-flooded (lubricated) single or multistage (generally from 15 hp to 500 hp) but have lower operating efficiencies at part-loads and also high unload power, which could become the key factors in reducing your operating efficiencies. However, incorporating VFD (variable frequency drive) or HPM motor (hybrid permanent magnet) would make these compressors efficient throughout the operating range.

Advantages of the rotary screw compressor include smooth, pulse-free air output in a compact size with high output volume over a long life.

Dynamic compressors Dynamic compressors impart velocity energy to continuously flowing air or gas by means of impellers rotating at very high speeds. The velocity energy is changed into pressure energy both by the impellers and the discharge volutes or diffusers. In the centrifugal-type dynamic compressors, the shape of the impeller blades determines the relationship between air flow and the pressure (or head) generated.

Centrifugal compressors

A centrifugal air compressor has a continuously flowing air stream which has velocity energy, or kinetic energy, imparted to it by an impeller, or impellers, which rotate at speeds that can exceed 50,000 revolutions per minute (rpm).

Three stage centrifugal compressors available in the market would give much higher efficiencies generally 10-15% more than the two stage positive displacement types.

Moreover, features like 100% oil-free air, constant pressure, high turndown abilities with good part-load efficiencies, nil wear & tear, much lower maintenance costs have made this compressor very popular with all users.

These are available from 250 hp to 5,000 hp and upward as well.

Compressor used in Textile Industry: Reciprocating type of compressors were normally in use in the textile industry.

However, of late screw compressors are being preferred as these are more energy efficient as compared to reciprocating compressors.

For very high capacity requirements centrifugal compressors are used. In fact, for many large textile units who have been using positive displacement technology for the last 5-10 years or above can ideally look to incorporate the centrifugal technology, which will have payback of less than 2 years in most cases.

Capacity range of air compressorsThe compressor capacity is stated in terms of cfm i.e. cubic feet per minute of air (being compressed or free air delivery). Capacity range of air compressors normally used in the industry is as follows:

Type of Air Compressor Capacity Range (cfm)

Reciprocating Compressor, Single Stage

Upto 50 cfm

Reciprocating, Two Stage 50-600 cfm

Screw Compressors 150-2500cfm

Centrifugal Compressors 2000-4000cfm

Optimization of Air System The six steps to optimize an air system are following.Demand Side1.  Establish your correct air needs for the points-of-use (Flow & Pressure)Distribution Side2.  Establish the leakage in your system and proactively manage the same3.  Analyse the System Capacitance & optimize the same.

4.  Track the pressure profiles across the plant to match the supply & demand and also minimise the pressure dropsSupply Side5.  Evaluate the health of the compressors and the support systems6.  Optimise the controls to match the system dynamics

Optimization of Air System

Minimizing Compressed Air Cost Compressed air cost can be minimize broadly in two ways

1. By minimizing wasteful consumption of compressed air i.e. by preventing compressed air leakages.

2. By improving the efficiency of compressors.