Compressed air dehydration systems

Design Overview

Refrigerating section, condenser and electrical panel are assembled on a painted steel frame which is mounted directly on the top of the tank in order to facilitate access for maintenance and minimize downtime losses.

Compressed air vessel

Evaporator (and separator) and air-to-air heat exchanger are installed in tandem and enclosed in a single all-welded vessel to minimize overall dimensions, simplify certification procedure and reduce floor space occupied by the dryer.

Air-to-air heat exchanger

Hot and humid incoming air passes through the stainless steel pre-filter (backwashed) before entering the air-to-air heat exchanger to prevent corrosion at the dryer inlet which may lead to tube plugging problems. The air-to-air heat exchanger is meant to reduce the heat load on the cooling circuit, thus decreasing the overall dryer cost and its power consumption, by pre-cooling the incoming air and re-heating the outgoing air.

Evaporator

The ribbed-tube evaporator is designed to provide the maximum heat exchange rate at the minimum volume and minimum pressure drop.

Moisture separator

Efficient separation of moisture takes place as the air stream passes through the moisture separator made of a fine-mesh stainless steel screen.

Refrigerator compressor

Two fully sealed Copeland screw compressors (arranged in tandem) are designed to provide failure-free operation with a high output capacity (130 to 225 m³/min) in any operating condition without risk of refrigerant contamination due to the closed-circuit loop design. Semi-sealed reciprocating compressors are used in the two latest models (280 m³/min to 350 m³/min).

Condenser

Standard dryer package includes a finned-tube, water-cooled condenser to minimize area requirements and provide increased heat transfer efficiency.

Refrigeration circuit

Refrigeration circuit incorporates the following standard equipment:

• Suction accumulator to prevent ingress of liquid refrigerant in the compressor
• Liquid filter/dryer with removable shell
• Gauge glass
• High and low pressure safety system
• CFC-free refrigerant R-407C
• Pressure-relief valve.

Electric circuit

Air dryers are fed from standard 400V/3-phase/50Hz supply mains without neutral wire. Built-in transformer provides 230V/1-phase/50Hz auxiliary power supply for two tray heaters, as well as 24V and 10V power supply for microprocessor-based controller and components. Main and auxiliary power supply circuits are protected by automatic trips, both low-voltage leads of the transformer are provided with safety fuses.

Microprocessor-based control

Hiross’s unique microprocessor controller is pre-tuned at the manufacturer’s plant and delivered to the client ready for operation, with a high-contract B&W display for convenient information read-out. Keypad panel provides ready access to temperature and pressure readings. Warning (about potential troubles) and alarm (conditions under which dryer will trip automatically) signals and dryer performance reports are displayed on-screen using easy-to-understand symbols and messages.

Technical data:

Being unaware of your specific system conditions, we have picked two models having different working pressures. The final choice can be made after obtaining detailed system information:

Adsorptive Air Dryers

Air dryers of adsorptive type are used, when the desired dew point is -20°C, -40°C or lower. Such dryers produced by different manufacturers have a fairly similar design with the principal differences in the type and composition of adsorbent and the method of regeneration. The other parameters are determined by the flow, pressure and nature of medium (gas or air).

Operating principle of adsorptive air dryer is based on the adsorption of air moisture by desiccant as humid air passes through the dryer column. The second column in the meantime is used for adsorbent regeneration.

Nowadays manufacturers are using two principal regeneration methods – hot and cold. In cold regeneration method a certain part of dried air (15-25%) is drawn from the drying column for blowing down the regeneration column after which the air is discharged. When the main column becomes saturated with water, the columns will “change places”. The changeover is carried out by control valves which are actuated by timer signal or dew point sensor. Hot regeneration is a more substantial and economical method. Air dryers using hot regeneration method allow to achieve a greater degree of dehydration down to -40°C and lower dew points.

Hot regeneration process may be implemented through different techniques employed in the design of air dryer – the most common technique is illustrated in the example below. In some cases the heat resulting from the compression process may be even utilized in the compressor, however this is only practicable in certain compressor models, and the cost of such dryer will be considerably higher than the cost of “standard” model. Moreover, the gain in energy saving due to the heat recovery may appear quite insignificant in the total energy balance of compressor station, as the efficiency of the compressors proper may decrease.

COES Dryers

Dew point -40°C Adsorbent Activated alumina Duration of cycle 6+6 hours Working pressure 4.9 bar (g) Explosion protection class IP55 Working voltage 400V-3Ph-50Hz Control Electronic