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Detecting flameless combustion

Detecting flameless combustion

Detecting flameless combustion

(OP)
Dear Eng-Tipsters,
                 Help! I am stick in rural India commissioning a rice hull furnace. Due to the lack of propane we need to modify the start-up sequence to start with rice-hulls from cold. We have propane pilot burners monitored by a BMS as an ignition source and overall PLC control. My problem is how can I monitor combustion of the rice hulls in a safe (high integrity) manner when there is no flame when the hulls burn. There is IR, so I was wondering whether there is an IR as opposed to UV based combustion monitor. While the PLC can monitor the temperature in the furnace as a means of confirming combustion, it is a PLC and therefore considered too unreliable for the task. Ideally I want some type of monitor that can bee hardwired directly to a BMS. I suppose the same issue is faced by systems burning wood and biomass and waste that do not produce strong flames. Any assistance in this matter enabling me to go back home would be greatly appreciated.

TISM

RE: Detecting flameless combustion

(OP)
Dear Jcubed00,
              Thanks for thee lead. I might get home before christmas after all!

TISM

RE: Detecting flameless combustion

the purpose of flame monitoring is to prevent uncontrolled combustion in the event flame is lost or blown out.

you can use UV/IR or so-called flame rods (flame ionization)or temperature as a basis for the "flame out" interlock.

RE: Detecting flameless combustion

(OP)
Dear hacksaw,
             In this case I need to identify loss of combustion, particularly during start-up from cold. I like the idea of a temperature based solution which I assume looks for a continual increase in temperature as proof of combustion. If so, how is the bet way to interface such a strategy with a hard-wired BMS?

TISM

RE: Detecting flameless combustion



we had a similar problem to what you have desribed with wood-gasifiers.

the risk of un-controlled combustion with hydrocarbon gases and liquids refers to loss of flame unless the fuel is cut.

with solids, the situation is different.

use of hydrocarbon supplemental fuel complicates the issue .

with the propane burner,in this case, you need conventional flame out detection. there is no change if you require supplemental fuel 100% of the time, i.e. no change to the flame monitoring system and interlocks.

if you elect to switch off the supplemental firing after ignition of the solids, then you need to monitor bed temperature and/or the products of combustion. the choice of where to place those temperatures is a function of the mechanical equipment and safety review. at a minimum you need redundant temperatures.

as you have recognized, you will need to provide control logic that identifies where you are in the light-off process so that the low-temp/high-temp interlock can be appropriately engaged.

the temperaure interlocks can be hardwired, but the bigger issue is whether or not such changes should be made in the field or not. these are major changes, and they need to be formally documented (and reviewed, Hazop'd, etc.) as a design change. at that time you can identify the needs for using triple mode redundant plc's,hardwiring, or some combination.





RE: Detecting flameless combustion

(OP)
Dear Hacksaw,
             Thanks for the benifit of your wisdom. The resources avaiable here are limited but your comments about any changes being major and worthy of HAZOP are right on the money. But at least I have more options than I started with.

Best Regards,

TISM

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