Fired Heater
Heat transfer mechanism:
- Radiation: from the burners
- Convection: flow of gas and fluid carring heat
- Conduction: Heat transfered to solid
- Stack temperature should not be lower than condensation temp. of flue gas to avoid acid rain and corrosion
Incomplete combustion:
CH4+O2=CO(g)+H2O (CO: odourless, colourless, toxic and pollutant)
CH4+O2=C(S)+H2O
Low heating value of a fuel: the amount of heat released by combusting a specified quantity
LHV of methane: 50 MJ/kg
High heating value of a fuel: includes the latent hear stored in the vapourised water
Zigarre: it is a big vessel to separate the particles prior to the flare activities.
Flare purge gas (Stutzgast) means gas introduced between a flare header’s water seal and the flare tip to prevent oxygen infiltration (backflow) into the flare tip. For a flare with no water seal, the function of flare purge gas is performed by flare sweep gas.
Gas flare/flare stack (Fackelgas):
- a device for gas combustion: it has smoke and visibile flame and offers incomplete combustion and cannot be used withis 500 meters of residences.
- to protect pressure vessel
- flare gas (Fackelgas)+ Combustion= flue gas (Abgas)/containing CO2/H2O/O2/(NO/NO2 due to N2 in the air)/SO2 due to the combustion of particulates in the fuel
Incinerator/enclosed combustor/mobile incinerator (mobile Abgasverbrennung): it has no smoke and visibile flame and offers complete combustion and can be used withis 500 meters of residences.
Reduce emissions to the environment before sending to the atmosphere:
- Using catalyst or a NH3 (ammonia)/urea
- Flue-gas desulfurization
Molecular weight of flue gas (Abgas):
- it depends on the fuel for combustion
- CH4+3O2=2H2O+CO2
Air: 79% N2 and 21% O2
Product:79% N2, 14%H2O and 7% CO2: 28 (0,79)+18(0,14)+44(0,07)=27,72 gr/mol
It should be considered that there is a specific limit of CO2 by TA.Luft
Cheminey (Shornstein/Ausblasrohr):
- made of clay or metal
- height of cheminey influences ability to transfer flue gases (Abgas) to the atmosphere (natural draft due to density difference coming from different temperatures)
- using an ejector with steam or N2 or water through Bernoulli effect, in which reducing surface area causes high velocity and low pressure (vacuum)to transfer flue gas from flare stack
Flare is only desigend for emergency case not for normal operations.
If there is a flare, we have to give information to the Bezirksbehörde (district authority): D-Meldung Feuerwehr
Flaring and blowdown:
Flaring and blowdown is a required practice for safe plant operation during plant deviations. Its purpose is to dispose of waste gases and liquids from process equipment, by separating liquids from the waste gas and then burning those gases in a flare. Blowdown has a lower capacity than knock out drum. Knockout drum is an immersion tank.
Purge gas: It purges combustible gases from the system and supports the pressure so that no air/oxygen enters the system to protect explosion.
Why do Flares need steam? smokeless operation?
Steam is used in steam assisted flare tips to either achieve smokeless operation, maximize tip life, and/or to shape the flame depending on the flare tip technology applied.
As the steam penetrates the column of flare gas, the surrounding air is pulled into the flare gases as well. The corresponding turbulence created from the steam injection causes the components to rapidly mix. The air is then able to come in direct contact with the flare gas so that combustion can occur.
