The document discusses the instrument air and service air systems used in power plants. The instrument air system provides clean, dry compressed air for critical instruments and controls. It ensures air is free of contaminants that could impact performance. The service air system also provides compressed air but not to the same quality level as it is for non-critical uses. Key components of the instrument air system include air compressors, dryers, filters, pressure regulators, and distribution piping. The document also describes the process air dryers use to regenerate their desiccant materials, which involves purging moisture and re-pressurizing the dryer bed.

1. Power Plant Instrument (IA) and Service Air
(SA) System
Power Plant Instrument (IA) and Service Air (SA) System
1. Instrument (IA)
The instrument air system provides clean, dry, and compressed air for various
instruments and control devices used in the various plant processes. It is typically used
in applications where the air quality is critical, such as in the operation of pneumatic
instruments, control valves, and other equipment. The instrument air system ensures
that the air supplied to these instruments is free from contaminants, moisture, and oil,
which could otherwise affect their performance or cause damage.
2. Service Air (SA)
The service air system is designed to provide a source of air for general plant use. The
air is not filtered as thoroughly as instrument air, it refers to the compressed air system
that provides air for various utility and support functions within the plant. It is used for
non-critical applications and services that do not require the same level of air quality as
instrument air systems.
Instrument Air system components
1. Air Compressor: The air compressor is the main component of the instrument air
system. It compresses ambient air and supplies it at a higher pressure. Typically,
rotary screw compressors or reciprocating compressors are used for this
purpose.
2. Air Dryer: The air dryer removes moisture from the compressed air to prevent
corrosion and damage to the instruments. Common types of air dryers used in
power plants include refrigerated dryers, desiccant dryers, and membrane dryers.
3. Air Filters: Air filters are installed to remove particulate matter, oil, and other
impurities from the compressed air. They ensure that the air supplied to the
instruments is clean and free from contaminants.

2. 4. Pressure Regulators: Pressure regulators are used to control and maintain a
stable pressure in the instrument air system. They ensure that the compressed air
is supplied at the desired pressure range required by the instruments.
5. Air Receiver Tank: An air receiver tank is a storage vessel that provides a
reservoir of compressed air. It helps in maintaining a steady supply of air during
peak demand periods and serves as a buffer for the compressor operation.
6. Distribution Piping: The instrument air system consists of a network of
distribution piping that carries the compressed air from the compressor to the
instruments and control devices throughout the power plant. The piping is
typically made of materials such as steel or copper or GI pipes.
7. Instrument Air Dryer: In some power plants, an additional instrument air dryer
may be installed specifically for critical instruments or control systems that require
ultra-dry air. These dryers can provide extremely low dew points to ensure the
highest level of instrument reliability.
8. Instrumentation and Control Devices: Various instruments and control devices,
such as pressure gauges, flow meters, control valves, and pneumatic actuators,
are connected to the instrument air system. These devices utilize the compressed
air to measure and control different parameters within the power plant.
Air system components
These are some of the common components you would find in the instrument air
system of a power plant. The specific configuration and design may vary depending on
the plant's requirements, size, and operational needs.
Air dryer regeneration
Air dryer regeneration refers to the process by which an air dryer removes the
accumulated moisture from its desiccant material or other moisture-absorbing
media, allowing the dryer to continue effectively drying the compressed air. As
compressed air passes through an air dryer, it often contains moisture vapor. The
primary purpose of the air dryer is to reduce the dew point of the compressed air,
ensuring that it remains dry and free from moisture before it is used in various
applications or equipment.
Air dryer regeneration process
The regeneration process varies depending on the type of air dryer. In heatless
regeneration, the dryer utilizes a portion of the dry compressed air to purge the
moisture from the desiccant bed. In heated regeneration, a separate heat source,

3. such as electric heaters or external hot air, is used to heat the desiccant and drive
out the moisture. The specific steps and procedures involved in the regeneration
process can differ based on the design and manufacturer's specifications of the air dryer.
1. Pressure Relief: The first step in the regeneration process is to relieve the
pressure. This is typically achieved by closing the inlet and outlet valves of the
dryer and opening a pressure relief valve. By venting the compressed air to the
atmosphere or a lower pressure level and then closing the blow-off valve.
2. Purge Cycle Initiation: Once depressurization, the purge cycle is initiated. The
purge cycle involves starting the blower to start heating and then pre-cooling
through redirecting a portion of the dry compressed air from the outlet of the
dryer to flow in the reverse direction.
3. Purge Airflow: The dry compressed air flows through the dryer in the opposite
direction to the adsorption airflow. This counter-flowing air carries away the
moisture that was previously adsorbed.
4. Moisture Removal: As the purge air passes through the dryer, it collects the
moisture adsorbed. The moisture-laden purge air, now saturated with moisture, is
discharged from the dryer through a purge valve or exhausts port and stops the
blower then starts cooling.
5. Pressure Equalization: After the purge cycle, the airflow to the desiccant bed is
closed, and the desiccant bed is re-pressurized. This is done by opening the inlet
and outlet valves of the dryer and allowing the wet incoming compressed air to
flow through the desiccant bed. The pressure equalization phase prepares the
dryer for the next drying cycle.
6. Split Flow: In some air dryer designs, a split flow configuration is used to
optimize the regeneration process. In this step, a portion of the dry compressed
air is diverted for the regeneration process, while the remaining portion continues
to supply dry air to the application. This allows continuous drying of the
compressed air while ensuring efficient regeneration of the desiccant bed.
Air dryer regeneration process
It's important to note that these steps provide a general overview of the air dryer
regeneration process. The specific steps and procedures can vary depending on the
type, design, and manufacturer of the air dryer being used. It's recommended to refer to
the manufacturer's instructions and specifications for the particular air dryer in use to
ensure the correct regeneration procedures are followed.