Operating and Maintenance Manual 09/2019 – part I
Screw compressors
16
5.3. ULTRA SPEED function – in screw compressors with motor power of 5.5
kW - 90 kW and frequency converter
This function regulate the speed so that the power currently consumed is close to the
nominal power of the engine. This results in rotation speed increase and thus capacity
increase at operating pressure lower then nominal pressure.
This function is implemented by a second PID regulator located in the inverter and
controlled by the DWEZ functionality.
The ultraspeed function enables higher compressor performance by setting a lower
operating pressure. It provides the maximum possible compressor capacity for a given
operating pressure while maintaining the nominal power of the device. The ultraspeed
function is especially useful at times of excessive demand for compressed air. In the
ultraspeed function, the main parameter managed by the controller is the main engine
power. Lowering the operating pressure below the nominal pressure, it is possible to
achieve higher capacity by increasing the speed of the main engine while maintaining the
nominal power. The scope of performance is presented in the Technical data table
contained in part II of the OMM.
5.4 Description of the compressed air treatment system
The system is the part of the compressor equipment mounted directly in the compressor.
The system comprises the following:
Pre-filter
The pre-filter (type Q) is used to separate the oil emulsion and solid contaminants
from the compressed air. High porosity of non-woven fabric, which the cartridge is
made of, ensures high dust collection ability, which guarantees the removal of
99% of solid and liquid particles larger than 3 µm (3-rd class in accordance with
ISO 8573.1). The particles together with condensate flow down to the filter tank
bottom and are removed automatically from there by the condensate drain.
The oil content does not exceed 0.6 mg/m3
Refrigerant dryer
It is used to clean compressed air. Owing to cooling the compressed air to low
temperatures (to the required dew point), the dryer precipitates condensate and
removes it. The air relative humidity, that is 100% before drying, drops to 21%
downstream the refrigerant dryer (for dew point of +3ºC).
The compressed air at temperature of +30ºC ÷ +45ºC, supplied to the dryer, is
initially cooled in the air to air exchanger to temperature of +14ºC ÷ +23ºC. Then
the air in the evaporator of the cooling circuit is further cooled and reaches the set
temperature of dew point of +3ºC, required to condense water vapour present in
the compressed air circuit.
Further precipitation of water and oil occurs in the dryer (downstream the pre-
filter). The dryer ensure to reach the point of dew of +3ºC (5.92 g of water/m
3
).
The precipitate condensate is removed outside with the conduit.
The detailed description of the dryer is included in the operating manual of the
dryer attached to the compressor documentation.
Operation:
The gaseous refrigerant coming from the evaporator (4) is sucked by the
refrigeration compressor (1) and it is pumped into the condenser (2). This one
allows its condensation, eventually with the help of the fan (3); the condensed
refrigerant passes through the dewatering filter (8) and it expands through the
capillary tube (7) and goes back to the evaporator where it produces the
refrigerating effect. Due to the heat exchange with the compressed air which
passes through the evaporator against the stream, the refrigerant evaporates and
goes back to the compressor for a new cycle.
The circuit is equipped with a bypass system for the refrigerant; this intervenes to
adjust the available refrigerating capacity to the actual cooling load. This is
achieved by injecting hot gas under the control of the valve (9): this valve keeps
constant the pressure of the refrigerant in the evaporator and therefore also the
To Next Page
Loading...