Algas SDI VAPORAIRE M-Series, Operation & Maintenance Manual

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Introduction
1-2
Algas-SDI Operations & Maintenance Manual – P/N - 54264
MIXER OPERATION - LPG-VAPOR/AIR MIXING PROCESS
LPG-vapor from a vaporizer enters the mixing system through a header manifold,
which distributes the gas to each venturi. A solenoid valve at the manifold
controls the flow of vapor to each venturi and a pressure switch monitors the
vapor pressure in the header. The venturi solenoid opens, feeding LPG-vapor
through a pressure regulator and then through the venturi nozzle. The LPG-
vapor creates a pressure lower than atmospheric pressure in the venturi housing
as it exits the venturi nozzle. Each venturi mixing train has a manual valve, so it
can be shut off separately.
The natural atmospheric pressure will force the air into the housing. Both air and
LPG streams are mixed and compressed in the diffuser section. The discharged
gas is then stored in the surge/accumulator tank as mixed gas. When the
pressure in the surge/accumulator reaches a preset level the venturi solenoid
valve will close. As the mixed gas is drawn off and used the mixed gas pressure
will decrease allowing the venturi solenoid valve to reopen. The system
maintains the mixed gas at a specified pressure in the surge/accumulator tank by
turning the venturis on and off within a small pressure deadband. This process
continues until the unit is switched off or shut down by a safety condition.
LPG-VAPOR/AIR MIXING PROCESS
See VAPORAIRE Mixer: Figure 1
Mixed gas is produced by the venturi assembly (5). LPG vapor enters the vapor
manifold and passes through the safety inlet solenoid valve (1). A High Mixed
Gas Pressure Switch in the explosion proof control box (9) monitors mixed gas
pressure within the surge/accumulator tank. If this pressure exceeds the normal
mixed gas delivery pressure, the mixer shuts down and the safety solenoid valve
will close, stopping LPG vapor flow into the mixer.
The
SEQUENCER
is a Programmable Logic Controller (PLC) that monitors
pressure in the surge/accumulator tank via a 4-20mA signal from a pressure
transmitter. The
SEQUENCER
controls 1 - 10 venturi valves. As the mixed gas
pressure decreases, the
SEQUENCER
energizes the number of solenoid valves
necessary to re-establish the proper mixed gas pressure. The
SEQUENCER
controls the rate and sequence at which the solenoid valves are turned on and
off. The venturi solenoid valve (3) energizes upon command from the
SEQUENCER
to allow LPG vapor to enter the venturi(s).
High pressure LPG vapor accelerates through the venturi nozzle (17) forming a
vacuum at the air inlet (19), which draws in air, mixing it with the vapor at a
specific rate. The mixed air/gas is propelled into the diffuser (18) where it
decelerates and gains pressure as it fills the mixer surge/accumulator tank. The
mixed gas is held in the surge/accumulator tank at the pressure set by the
SEQUENCER
until withdrawn through the mixed gas discharge valve.
Single venturi mixers use one venturi with a pressure switch for control to mix
LPG vapor and air which is distributed to the surge/accumulator tank.