Hi-Lo Enclosed Landfill Flares can be tailored to suit customer
requirements.
www.Hilogroup.com: Minefield Degassing
General Philosophy
High Temperature Enclosed Flare
Gas enters the unit prior to starting gas booster if needed.
Ignition State
Flare tip and vents set to starting position flow control valve opens to
represent ignition flow set point. Gas inlet monitors – monitor the
gas once the correct levels are reached the ignition sequence is able to
work. Once the flare gas is alight, temperature rises above set level, the
flame is established the igniter stops, pilot constant flame or timed.
Increase State
Increase flow automatically by pressure levels or manually.
Cone motor and air vents position to suit flow and to produce ideal
operating temperatures.
Once a main alarm is reached the unit shuts down. Solenoid valves for
pilot gas close if on constant pilot, pilot shut down. Solenoid valves for
slam shut closes booster shuts down, flow control valve to default
position i.e. closed, alarms indicated.
Flame temperatures must be below set point before ignition sequence will
operate to re-light flare.
Acknowledge alarms – attempt re-light.
Gas Booster
If the gas needs to be extracted from the minefield a gas booster is
provided to suit the amount of pressure and flows required. This booster
will automatically start/stop inline with the start sequence or alarm
situation.
Slam Shut Valves
On a safety aspect, slam shut valves are fitted in the process line
after the fan which are controlled by a solenoid valve. These open when
the gas booster is started and slam shut during any shut down or alarm
situation.
Inlet Gas Monitors
Inlet gas monitored CH4, CO2, O2 or
the main combustible gases. These are the main gases monitored on inlet
and are connected to the control system.
Alarm levels are entered to achieve safe levels for flaring.
I.e. O2 < 1%, CH4 > 20%.
The unit is unable to ignite until these set points are reached, also
during running sequence if these are breached the unit automatically shuts
down.
Ignition Sequence
Once start flow set point is reached and the inlet gas analyser reaches
set points of gas levels.
Solenoid valve for stack opens to give pilot gas to stack – igniter
flashes for set time period lighting pilot and in return lighting main
gas.
Ignition system will not work until gas levels are reached or flow level
reached as to set points.
Igniter may try this a set number of times until the flame temperature
exceeds its set point.
Set point target = flame established.
Lamp lights on control cabinet to indicate stack flame established.
Flow can be increased.
Pilot can be a continuous or timed type.
Flow Control Valve
Power operated control valve operated by the PLC System manually by
increasing percentage open or closed.
This again is designed to be automated so that the flow will
automatically decrease / increase inline with the pressure of the inlet
gas. A pressure transmitter indicates to the PLC the amount of inlet
pressure which after pre-commissioning works can control the correct
amount of flow of gas to the flare that the field produces.
Cone Operation/Variable Tip
Flare tip cone can be operated via the control panel, up or down as a
percentage.
The tighter the cone to it’s seat the more velocity on the inlet
gas.
These are normally pre-set on a set percentage that suits starting flows
for ignition and normal running flows and can be automated to be at the
best position to suit variable flows after a commissioning period.
Vent Operation
Each stack has vents at the base of the stack for natural airflow. These
can be opened or closed respectively (but not completely closed).
Higher Flow
More Vent
Lower Flow
Less Vent (less vent can also increase flue temperature)
These can be hand operated or motor operated which then can be automated
after commissioning period.
Flow Reading
A differential pressure transmitter is fitted to the unit connected to a
flow tube or torbar in the flow line.
This gives a 4-20mA signal, which the control screen reads as an actual
flow in m3/hr.
Flame Establishment
Flame establishment is achieved by means of thermocouples.
There are two thermocouples installed in the stack, one at the bottom to
read the flame temperature and the other at the top to read the flue
temperature, they are 0-1200°C rated and give a 4-20mA signal back to
the control panel which gives a temperature reading in oC on the display
screen.
Flame temperature will be the indication for flame establishment >
temperature set flame lit < temperature set point flame out.
The flue temperature will be the indication for the exhaust emissions.
The ideal temperature for the flue will be around 1050°C –1110°C
that minimises most emission gases. This temperature is achieved by
opening and closing air vents at the base of the stack the greater they
are opened the more air intake lowering the temperature.
This reading is also displayed on the display screen but does not produce
any alarms.
The set point is a determined figure to suit site and operating
conditions.
Alarms
Alarms situation would be for example: -
O2 > 1% CH4 < 20% Depletion of gas flow < 300m³/hr ESD pushed Power Failure Flame temperature < 150°C
All the above would result in complete shut down Flashing beacon on top of unit operates Audible alarm on unit operates Lamp on unit door illuminates
All alarm connections could be provided for the customer.
Flame Arrestor
A flame arrestor is fitted in the main flow line as a safety feature.
