Industrial furnace
The dry oxygen content in the exhaust of an industrial furnace may be controlled to 1% or less by determining one or more of: the temperature of: each or a group of one or more burner (flame); one or more section of the radiant walls adjacent (e.g., within 5 feet of the burner); the temperature gradient across the process coils; the combustion products of one or more burners; the mass flow rate or the volume flow rate of air to each burner (e.g., the pressure drop across the variable forced air aperture ii) comparing the result to said target value; and iii) adjusting either a) the opening of the variable forced air aperture; or b) adjusting the mass flow rate or the volume flow rate of air from said one or more fans.
1. A method for controlling the air flow to one or more burners in a balanced forced air draft ethylene cracking furnace comprising
one or more coils receiving a feed of ethylene, said coils passing through a convection section in a furnace arch or exhaust and then through a radiant section having one or more radiant walls at a temperature from 800° C. to 1200° C.,
one or more fans, feeding air to one or more common air ducts leading to an array of two or more burners for burning a gaseous fuel,
each said one or more burners drawing combustion air only from said one or more common air ducts and being associated with a variable forced air aperture and a flow controller there for having a control fidelity of 1% of said air flow at its maximum flow rate, and
a probe to measure the air pressure drop across the flow controller so that the oxygen content in the exhaust gas at the furnace arch is from 0.5 to 1% dry oxygen and the distribution of said air flow to each said one or more burners is at a target value,
the method comprising:
i) measuring one or more of:
a) the temperature of one or more burner flames;
b) the temperature of one or more section(s) of said one or more radiant walls adjacent to said one or more burners, wherein said section is within 5 feet of said burner;
c) the temperature gradient across said one or more process coils;
d) one or more combustion products produced by said one or more burners;
e) a mass flow rate or a volume flow rate of said air flow to each burner; and
f) the air pressures drop across the flow controller,
ii) comparing said measurement to target value(s);
iii) making an adjustment, to one or more of:
a) the opening of said variable forced air aperture; or
b) said mass flow rate or said volume flow rate of said air flow from said one or more fans to achieve said oxygen content from 0.5 to 1% of dry oxygen in said exhaust gas at said furnace arch.
2. The method according to claim 1 , wherein said air flow to each said one or more burners is controlled to achieve said oxygen content of 0.8% dry oxygen or less in said exhaust gas.
3. The method according to claim 1 , wherein said variable forced air aperture comprises a mechanical iris.
4. The method according to claim 1 , wherein said variable forced air aperture comprises a damper.
5. The method according to claim 1 , wherein said variable forced air aperture comprises two or more ½ moon shaped discs on a common pivot point movable relative to each other.
6. The method according to claim 1 , wherein said variable forced air aperture comprises two or more ¼ moon shaped discs on a common pivot point movable relative to each other.
7. The method according to claim 1 , wherein said variable forced air aperture comprises two or more plates having multiple holes having a diameter of ¼ inch or less in each plate; said plates being rotatably mounted relative to each other and rotating said plates increases or decreases said air flow.
8. The method according to claim 1 , wherein said variable forced air aperture comprises a valve.
9. The method according to claim 1 , wherein said measurement(s), from step i), is fed to a microprocessor having been programmed with said target value(s), a software compares said measurement to said target value and said microprocessor communicates with said controller to make said adjustment, wherein said adjustment increases or decreases the opening in said variable forced air aperture to achieve said target value.
10. The method according to claim 1 , wherein said measurement(s), from step i), is obtained by one or more probes at the point of measurement.
11. The method according to claim 1 , wherein said measurement(s), from step i), is obtained by one or more devices distant from the point of measurement.
12. The method according to claim 11 , wherein said devices are selected from the group consisting of lasers and cameras.
13. The method according to claim 1 , wherein said target value is defined by an initial set up of the furnace.
14. The method according to claim 1 , wherein said target value is defined by an air requirement of each burner at its fuel consumption rate.
15. The method according to claim 1 , wherein said target value is defined by an air/fuel ratio requirement for each burner, given a fuel gas composition.
16. The method according to claim 1 , wherein said measurement(s), from step i), is taken on a periodic basis from once per second to once every 30 days.