Membrane Systems for Adsorption and Regeneration Cycle Problems in Air Drying Unit

Membrane Systems for Air Drying Unit

Bachelor Thesis 2008 56 Pages

Engineering - Chemical Engineering


Table of Contents


List of Tables

List of Figures

List of Acronyms


1. Introduction
1.1 Background
1.2 Objectives
1.2.1 General objective
1.2.2 Specific Objectives

2. Literature Review
2.1 Accessories
2.1.1 Compressor
2.1.2 After Coolers
2.1.3 Separators
2.1.4 Prefilter
2.1.5 Dryer
2.1.6 After Filter
2.1.7 Receiver
2.2 Air Drying Unit
2.2.1 Specification of Drying Unit
2.2.2 Inlet Condition
2.2.1 Outlet Condition
2.2.3 Cycle Time
2.2.4 Filter
2.2.5 Adsorption Cycle
2.2.6 Regeneration & Service Cycle Change Over
2.3Air Dryer
2.3.1 Dryer Selection
2.4 Expected Outcome
2.4.1 Membrane Dryer
2.5 Balston Compressed Air Dryers
2.5.1Membrane Air Dryers
2.5.2 Application
2.5.3 Compressed Air Dryers
2.5.4 Application
2.5.5 Importance of Moisture Removal
2.6 Membrane Filtration Technology
2.6.1 Eliminating Downtime and Reducing Maintenance
2.7 Hankison Membrane Compressed Air Dryers
2.7.1Advantage of Hankison membrane dryer
2.7.2 Choice of Prefilter Package
2.8 Parker Membrane Air Dryer
2.8.1 Membrane Air Dryers for Analytical Instruments - Dry Air on Demand, Up tp 1,203 lpm
2.8.2 Principal Specification
2.8.3 Flow Rates (lpm)
2.9 Prism Membrane Low-Pressure Air Drying
2.9.1 Benefits
2.10 Types of Membranes
2.10.1 Isotropic membranes
2.10.2 Nonporous, dense membranes
2.10.3 Electrically Charged Membranes
2.10.4 Anisotropic membranes
2.10.5 Ceramic, Metal and Liquid Membranes
2.11 Maintenance

3. Working / Implementation of the Project Work/ Simulation
3.1 Cost Estimation in Membrane Air Dryer
3.1.1 Estimated Energy Costs
3.1.2 Actual Energy Cost
3.1.3 Labor Cost
3.1.4 Handling Costs
3.1.5 Estimated Fixed and Capital Costs
3.1.6 Actual Capital Cost
3.1.7 Actual Fixed Cost
3.1.8 Total Drying Cost
3.1.9 Dry or Market Wet
3.2 Cost Estimation

4. Result Analysis
4.1 Advantages of Membrane Dryers
4.2 Disadvantages of Membrane Dryers
4.3 Comparison of Dryer

5. Conclusion



Appendix A: Water Content of Air at Various Temperatures and Pressures (Compressed air and gas institute, 1998)

Appendix B: Moisture Content of Saturated Air at Various Temperatures(Compressed air and gas institute, 1998)

Appendix C: Dew Point Conversion (Compressed air and gas institute, 1998)

List of Tables

Table 1.1 Inlet condition

Table 1.2 Outlet condition

Table 1.3 Cycle time

Table 1.4 Filters

Table 2.1 Parker membrane air dryer specification

Table 2.2 Parker membrane air dryer flow rates

Table 3.1 Comparison of dryer

List of Figures

Figure 1.1 Components of a typical industrial compressed air system

Figure 2.1 Compressed air dryer

Figure 2.2 Membrane dryer

Figure 2.3 Balston compressed air dryers

Figure 2.4 Series membrane air dryers for +35°F (+2°C) Dewpoint

Figure 2.5 Prism membrane low-pressure air drying

Figure 2.6 Isotropic membranes

Figure 2.7 Nonporous, dense membranes

Figure 2.8 Electrically charged membranes

Figure 2.9 Anisotropic membranes

Figure 2.10 Ceramic, metal and liquid membranes

Figure 2.11 Ceramic

List of Acronyms

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I wish to express my sincere gratitude and earnest appreciation to my research advisors, Mr. Moges Ashagrie and for his guidance, advice, patience, and encouragement in the development of this project and for their assistance in the preparation of this manuscript

It is my pleasure to express my sincere appreciation to my mother, Teje Tefera and my sister Worknesh Atnafu for their unconditional love and support in my education


Main problem in air drying unit is the adsorption and regeneration time. In a dryer adsorption continues for eight hours, after which the desiccant becomes saturated and cannot adsorb further moisture. In this study different types of desiccants are used. Instead of silica gel, activated alumina, zeolite, molecular sieves, activated carbon were used. Membrane dryer are used to solve our regeneration problem. Therefore membrane air dryer is more optimum for commercial processes than the other different dryers. Membrane dryer can be used for 24 hours for one week, so there is no need to standby this equipment. The construction and operation cost of membrane dryer is too simple and can also be used in hazardous condition.

Keywords:Adsorption time, Regeneration time, Activated carbon, Membrane dryer

1. Introduction

1.1 Background

Compressed air systems may be noisy, but they are necessary. While they may look intimidating, most modern compressed air system are composed of similar major sub-systems and many sub-components. This document is intended to provide you with the basic information about modern compressed air systems (Golden et al., 2000).

Major compressed air sub-systems include the compressor, prime mover, controls, treatment equipment and accessories, and the distribution system. The compressor is the mechanical device that takes in ambient air and increases its pressure. The prime mover powers the compressor (typically the electric motor). Controls serve to regulate the amount of compressed air being produced. The treatment equipment removes contaminants and water from the compressed air, and accessories keep the system operating properly. A distribution system consists of the piping that is analogous to wiring in the electrical world they transport compressed air to where it is needed. Compressed air storage can also serve to improve system performance and efficiency (U.S department of energy,2003).Figure 1.1 shows a representative industrial compressed air system and its components.

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Figure 1.1 Components of a typical industrial compressed air system (U.S department of energy, 2003)

The compressor consists of main two parts L.P & H.P. L.P means low pressure and H.P means high pressure cylinder. In the operation of compressing air, first of all atmospheric air is become a suction of first stage. In the L.P cylinder, the atmospheric air is compressed at 3 kg/cm2 and the temperature is rises up to 130 0c. After compressing of air from L.P the compressed air is passed through inter cooler for removal of heat from air. In the inter cooler the temp of compressed air is down up to 300c. And then it is suction for the hp cylinder, here the pressure is rises up to 7.5 kg/cm2 and temperature is increased up to 1200-1350 c. After the compressed air cooled by after-cooler & temp is decreases at 300c. And this compressed air is fed in the three parts for instrument air, itemizing air, and process air (U.S department of energy, 2003).

1.2 Objectives

1.2.1 General Objective

The general objective of this research project is application of membrane systems for absorption and regeneration cycle problems in air drying unit.

1.2.2 Specific Objectives

- To study about modern compressed air systems
- To identify the best dryer for commercial purpose
- To estimate the costs of the dryer

2. Literature Review

2.1 Accessories

Accessories are the various types of equipment used to treat compressed air by removing contaminants such as dirt, lubricant, and water; to keep compressed air systems running smoothly; and to deliver the proper pressure and quantity of air throughout the system. Accessories as shown in figure 1.1 include compressor after coolers, filters, separators, dryers, heat recovery equipment, lubricators, pressure regulators, air receivers, traps, and automatic drains. In air drying unit clean, dry compressed air plays an essential role in industry with many applications, and is often considered a fourth utility at most facilities. It is used to move conveyors, transport products, power pneumatic tools, automate equipment, operate critical instrumentation, packaging, and for process operations. The compressed air drying process includes many equipment components including filters. Their performance has an effect on the degree of dryness and cleanliness of the compressed air (Kerry et al., 1991).

2.1.1 Compressor

Atmospheric air is compressed to a desired discharge pressure level for downstream use (Kerry et al., 1991).

2.1.2 After Coolers

Mechanical energy is applied to a gas for compression so that the temperature of the gas increases. After coolers are installed, the final stage of compression to reduce the air temperature. As the air temperature is reduced, water vapour in the air is condensed, separated, collected, and drained from the system. Most of the condensate from a compressor with intercooling is removed in the intercooler(s), and the remainder in the after cooler. Almost all industrial systems, except those that supply process air to heat-indifferent operations require after cooling. In some systems, after coolers are an integral part of the compressor package, while in other systems the after cooler is a separate piece of equipment. Some systems have both (Kerry et al., 1991).

2.1.3 Separators

Separators are devices that separate liquids entrained in the air or gas. A separator generally is installed following each intercooler or after cooler to remove the condensed moisture. This involves changes in direction and velocity and may include impingement baffles. Lubricant-injected rotary compressors have an air/lubricant coalescing separator immediately after the compressor discharge to separate the injected lubricant before it is cooled and recirculated to the compressor. This separation must take place before cooling to prevent condensed moisture from being entrained in the lubricant (Golden et al., 2000).

2.1.4 Prefilter

A coalescer designed to remove fine oil and water mist aerosols still remaining to prevent the fouling of the desiccant bed in the dryer. Common prefilter ratings are 0.3 to 1 micron (Dyer, 1988).

2.1.5 Dryer

Desiccant or refrigerated dryers are common designs to remove the remaining water vapour from compressed air. A dual tower desiccant dryer provides the most effective moisture reduction. Dryness is achieved by dew point suppression and reduces further potential for moisture condensation in downstream piping (R.H. Perry et al., 1997).

2.1.6 After Filter

A particulate filter to remove desiccant dust that may carry over from the dryer, usually rated for 1 to 3 micron particulates removal (Kerry et al., 1991).

2.1.7 Receiver

Provides storage capacity to meet peak air demand and dampen compressor pulsations (Kerry et al., 1991).

2.2 Air Drying Unit

In Fertiliser Company there are two air drying units: one unit is adsorption unit and the second one is regeneration unit. At one time, compressed air dryers were luxuries. Today, as maintenance costs continue to rise and the need for increased productivity grows, they’re a necessity in nearly every process where compressed air is used (R.H. Perry et al., 1997).

2.2.1 Specification of Drying Unit

Gas: compressed air

Source of supply: non lubricated compressor (R.H. Perry et al., 1997).

2.2.2 Inlet Condition

Table 2.1 Inlet condition (Gemmingen, 1994)

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There are two air drying units. The first unit is air drying unit-A and the second is air drying unit-B. It consists of two cycles:



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Bahir Dar University – Engineering Faculity
membrane systems adsorption regeneration cycle problems drying unit



Title: Membrane Systems for Adsorption and Regeneration Cycle Problems in Air Drying Unit