Small receiver mounted compressors are used in many applications that require clean dry air in order to operate safely, effectively and reliably whilst minimising energy consumption and maximising the volume of compressed air available at the critical point of use.

Recent technology developments offer a step change in the purification of the compressed air. This paper reviews currently available solutions and the potential for the use of Air Purification Skroll technology.

www.apskroll.com

INTRODUCTION

Air Purification and Dehydration for Small Receiver Mounted Compressors

Many areas of our everyday life are touched by compressed air with applications in laboratory, medical, dental, food and beverage, and other critical uses requiring clean and dry compressed air.

One of the challenges facing compressor manufactures and packagers of these compressor systems, is to make their systems simple and reliable. Current technologies can be expensive, complex and wasteful of energy. High dryer purge rates can result in significant loss of compressed air available for the application with possible catastrophic consequences.

Condensed water vapour within the compressed air system is by far the major contaminant which, if left untreated, leads to the malfunction of equipment, corrosion, product spoilage and bacterial growth. Typically, 1 litre (1US Quart) of water needs to be removed daily.

A technology that allows the user to determine the dryness of the air to suit their requirement while maintaining stable Dew Point Suppression (DPS) or % Relative Humidity (RH) over a wide range of conditions is desirable. A technology that is highly efficient, reliable, requires no maintenance, has low installation and operating costs, is even more desirable.

Compressed air from small non-lubricated compressors contains condensed water, water vapour and particulates, which need to be removed before use. ISO8573.1 specifies air quality standards for these contaminants of which water is the biggest problem.

Atmospheric air, for example, at 40°C (104°F) and 65% relative humidity, contains 33.2g/m3 of water vapour. Following compression to typically 7barg (100psig), air is discharged from the compressor via an air-cooled after-cooler, the discharge temperature will be typically 40°C (104°F) and 100% relative humidity containing 3.8g/m3 of water vapour. The bulk water (condensate) is removed by simple filtration but the water vapour needs to be removed by a dryer.

For a 0.55kW (0.75hp) compressor with a 40% load duty discharging 75Nl/min (2.7scfm) of compressed air, over 4,000 hours annually; the total water condensate and vapour is 238 litres, about 1 litre (1 US Quart) of water per day. All of this water condensate and most of the vapour must be prevented from entering the system to eliminate damage to downstream equipment, contamination of product, corrosion and bacterial growth.

COMPRESSED AIR PURIFICATION

Author:

Abstract:

Colin Billiet - Owner of APSL & Former CEO of the domnick hunter group PLC.

www.apskroll.com

Skroll adsorption media technology is a unique adsorption medium. It is best described as an adsorbent sheet (typically 1mm in thickness) consisting of a high level of adsorbent and utilising a durable polymer binder which produces fast adsorption/desorption kinetics and low energy use. When Skroll technology is incorporated into a compressed air dryer it provides a very robust long life product. Skroll’s durability ensures that even if flooded with water condensate or subjected to excessive air flow, it will (once normal conditions are resumed) fully recover its performance. Skroll’s polymeric binder ensures high chemical resistance (a known issue with semi-permeable membranes) and does not shed dust (a known issue with desiccant beads). Skroll media provides extremely stable dew-point suppression anywhere between that achieved by refrigerated and desiccant dryers.

SKROLL ADSORBENT TECHNOLOGY

Air Purification Skroll adsorption media is revolutionary (patents pending). It consists of adsorbent crystals immobilised in a durable polymer support structure, it is produced in the form of a continuous sheet. When converted into a Skroll construction, flow paths are created between layers. This enables optimum performance to be achieved in applications such as dehydration of air and gases. It is tough and durable, recovers from misuse and has a long service life.

Systems currently available include refrigerated, membrane and desiccant dyers.

Refrigerated Dryers: Small applications are expensive, bulky and require specialised maintenance. Pressure dew point typically limited to +10°C (50°F)

Membrane Dryers: Continuous purge air requirement can be up to 30%. Life of the membrane is limited and costly, making a high level of inlet filtration essential. Continuous purge results in unnecessary compressor use, reducing compressor life significantly. If the membrane is depressurised with the start stop of the compressor, fatigue of the delicate membrane fibre leads to breakage and loss of air supply. Membrane can be prone to chemical attack, suffer catastrophic failure due to shock and vibration, and maintenance costs can be high.

Traditional Desiccant Adsorption Dryers: Heatless dryers are used due to their simplicity of design, but purge air losses can be up to 25%. Suitable for stable applications where very low dew points may be required (-40°C/F) and access for maintenance is convenient. However the high level of expensive inlet and outlet filtration, and essential servicing can be problematic.

SYSTEMS CURRENTLY AVAILABLE

WEI

GH

T PE

RC

ENT

ADSO

RBE

D /

%

RELATIVE HUMIDITY / %

0

5

10

15

20

25

30

0 20 40 60 80

ADSORPTION AT 30°CDESORPTION AT 30°C

Water adsorption isotherm shows the Skroll material has a high affinity for water even at low % RH, with uptakes of 20% wt at <10% RH.

The Skroll material reaches an adsorption equilibrium at 25% wt which can easily be recovered via desorption as shown in the desorption profile.

High Adsorbent Capacity Skroll Media Dust Free, Water Tolerant

Air Purification Skroll

PROCESSED AIR PURGE AIR

OUTLET AIR

AIR RECEIVER

• High continuous purge loss of 15 to 30%• Significant pressure loss up to 1 bar (15psi)• Loss of available air• Typically 2 inlet filters required• A 3rd carbon filter is often specified• Float type auto-drains may fail and require service • Repeatedly depressurising of membrane - fatigue risk• Total loss of air if membrane fails

MEMBRANE SYSTEM

• High pressure loss typically 0.7bar (10psi)• High purge air loss up to 25%• Loss of available air• Float type auto-drains may fail and require service• Typically, 2 inlet filter plus a 3rd outlet dust filter• High service requirement• Expensive system controls and valving• Does not recover from misuse

TWIN TOWER SYSTEM

AIR PURIFICATION SKOLL SYSTEM• Lowest pressure loss typically 0.1bar (1.5psi)• 100% outlet flow when compressor is running• No service required• Lifetime guarantee• Reliable solenoid drain• Simple controller• Selectable dew point• Purge air <10% when compressor is off load• Fully recovers from misuse

Inlet Condensate Removal = Compact and Cost SavingSolenoid Drain = Reliability - No Servicing RequiredInlet Filter = Compact and Cost SavingSkroll Adsorbent Module = Robust with Lifetime GuaranteeOutlet Filter = Compact and Cost SavingNon-Return Valve = Compact and Cost SavingOutlet Flow Controller = Prevents Excessive Over Flow

INTEGRATED FEATURES & BENEFITS

MEMBRANE SYSTEM

OUTLET

PURGE

AIR RECEIVER

TWIN TOWER SYSTEM

OUTLETAIR RECEIVER

B

A

C

Built in Non Return Valve & Flow Control Orifice.

Inlet from oil-free compressor.No Filtration Required.Tangential Water Separation.

Timed exhaust solenoid valve (low back pressure) opens when compressor goes off load. Set timer to determine desired dew point.

A

B

C

Typically small receiver mounted compressors operate with a duty of 40% or less.

The SC Dryer will, at these conditions, produce a dew point suppression of 50°C or better with consistent performance over a wide temperature range.

The unique characteristics of Skroll media means that even if the compressor operates at a high duty, in excess of 60%, the fixed purge air requirement is less than 10%.

Note: The adjacent graph relates to a 5-7 bar pressure range and inlet temperature of >40°C.

DEW

PO

INT

SUPR

ESSI

ON

°C (°

F)

% PURGE

25(77)

30(86)

35(95)

40(104)

45(113)

50(122)

55(131)

19 18 15 13 1117 16 14 12 10

40 50 60COMPRESSOR DUTY %

AMBIENT: 40°C (104°F)INLET: 100% RH

FEATURES MEMBRANE SYSTEM

TWIN TOWER DESICCANT SYSTEM

AIR PURIFICATION SKROLL

Purge 15 - 30% ≈25% <10%

Integrated Pre-Filtration

Pressure Drop Up to 1 bar Up to 0.7 bar Less than 0.1bar

Resistant to Fatique / Dusting Breakdown

Resistant to Vibration

Number of External Filters Up to 3 Up to 3 0

Activated Carbon Filter Optional Extra Optional Extra Optional Extra

Produces Sterile Air Optional Extra Optional Extra

Fail Safe / Fully Recovers

Full Compressor Flow Avaiable

Variable Dew Point

Simple Installation / Integration

Life Time Guarantee

No Expensive Controller Required

Recovers from Misuse

PURGE PRESSURE DROP OUTLET FLOW %

MEMBRANE SYSTEM TWIN TOWER DESICCANT SYSTEM AIR PURIFICATION SKROLL

PATENTS PENDING - © Copyright 2018 - TP1.1 08/18

Air Purification Skroll LimitedDukesway, Team Valley Trading Estate, Gateshead, NE11 0PZ

Tel: +44 (0)191 495 8501 Email: enquiries@apskroll.comWeb: www.apskroll.com

AIR DRYER COMPARISON

Key attributes of Skroll medium include stable performance over its life time, and low purge rates. When conditions exceed the design parameters dew point suppression may reduce but will quickly recover performance. Total dew point suppression will not be lost unless flooding occurs but even then it will recover fully once normal operating conditions are stabilised.

The unique features and benefits of the new Air Purification Skroll medium have been explained in relation to existing technologies which should result in a bright future for it in the dehydration of air and gases. The single column dryer containing Skroll medium provides simplicity of installation, robust performance, long life, excellent value and is an attractive alternative to existing technologies.

SUMMARY