Continuous Pneumatic Regulating System - Atlas Copco XAS 400 JD IT4 HOP Instruction Manual

CONTINUOUS PNEUMATIC REGULATING SYSTEM

The compressor is provided with a continuous pneumatic
regulating system and a blow-off valve (BOV) which is
integrated in the unloader assembly (UA). The valve is
closed during operation by outlet pressure of the
compressor element and opens by air receiver pressure
when the compressor is stopped.
When the air consumption increases, the air receiver
pressure will decrease and vice versa. This receiver
pressure variation is sensed by the regulating valve (RV)
which, by means of control air to the unloader assembly
(UA), matches the air output to the air consumption. The
air receiver pressure is maintained between the pre-
selected working pressure and the corresponding
unloading pressure.
When starting the compressor, the throttle valve is kept
closed via receiver pressure. The compressor element
(CE) takes in air and pressure builds up in the receiver
(AR). The throttle valve is closed. The air output is
controlled from maximum output (100%) to no output
(0%) by:
1. Speed control of the engine between maximum load
speed and unloading speed (the output of a screw
compressor is proportional to the rotating speed).
2. Air inlet throttling.
If the air consumption is equal to or exceeds the maximum
air output, the engine speed is held at maximum load speed
and the throttle valve is fully open.
If the air consumption is less than the maximum air output,
air receiver pressure increases and the regulating valve
supplies control air to throttle valve to reduce the air
output and holds air receiver pressure between the normal
working pressure and the corresponding unloading
pressure. Unloading pressure = normal working pressure +
1.5 to 2 bar (22 to 29 psi).
When the air consumption is resumed, the blow off valve
(BOV) closes and the throttle valve gradually opens the air
intake and the electronic speed regulator increases the
engine speed.
The construction of the regulating valve (RV) is such that
any increase (decrease) of the air receiver pressure above
the pre-set valve opening pressure results in a proportional
increase (decrease) of the control pressure to the throttle
valve and the electronic speed regulator.
Part of the control air is vented to atmosphere, and any
condensate discharged, through the vent holes.
EXHAUST GAS AFTERTREATMENT
To meet the demands of EPA Tier4a/ EU Stage IIIB
Emission Legislation, the engine is equipped with an
exhaust gas recirculation system and a particulate filter.
The exhaust gas is fully automatically cleaned. The
process is monitored by the Xc2002 machine
controller.
STEP 1 EXHAUST GAS RECIRCULATION
With Exhaust Gas Recirculation (EGR), part of the
exhaust gases are cooled and then injected back into the
engine cylinders to reduce NOx.
Exhaust gas is cooled to allow the introduction of a greater
mass of recirculated gas.
The outcome is a lower peak combustion temperature.
STEP 2 DIESEL PARTICULATE FILTER +
DIESEL OXIDATION CATALYST
To remove excess particulate matter from the exhaust gas,
a Diesel Particulate Filter (DPF) is used. This system
consists of a Diesel Oxidation Catalyst (DOC) and a filter
module. The DOC reduces CO, HC and NO through
oxidation. It also produces NO2 to regenerate the DPF.
The filter system removes 99% of particulate matter.
STEP 3 ACTIVE REGENERATION
Particulate matter left in the filter system is burned in a
process called regeneration. Extending the.lifetime of a
filter, it converts particulate matter into CO2 and ash.
Atlas Copco engines use high temperature regeneration
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that includes a fuel burner in the exhaust stream that
intermittently raises the temperature above 600º C /
1100° F.
Active regeneration decreases in the higher load cycles of
the compressor.
STEP 4 ASH REMOVAL
Additives in lube oil that do not combust during
regeneration, turn into ash. This reduces filter volume,
oxidation efficiency and backpressure.
Ash must be removed mechanically, according a service
interval, either by washing or blowing it out. This service
interval can be increased depending on duty cycle.