Designing an inline flare gas combustion chamber

[benjaminb]

I have built a nice biomass gasifier that produces about 700,000 btu's of heat per hour by burning or flaring the gas that comes out of it.
What I want to do is, to flare the gas in an enclosed chamber so I would be able to capture all the exhaust and run it through some heat exchangers for heating hot water.
I have a suction fan that pulls the gas out of the gasifier and then blows it into the flare/burn chamber and through the heat exchangers.
In order to save using another blower to blow air, (oxygen) into the flare/burn chamber, I meter it in on the suction side of the blower where it is mixed to the correct fuel air mixture.
This works great burning the gas in the flare/burn chamber into the open atmosphere. But when I put a lid on the chamber and force the exhaust to flow through pipes to the heat exchangers, then the flare doesn't want to stay in the burn chamber. It either jumps down the pipe through the blower right to where the oxygen inlet is, or it travels up the pipes from the burn chamber towards the heat exchangers.
I would like to figure out how to get the flame to stay in the burn chamber.
Does the burn chamber need to be larger?
Does the inlet pipe need to be smaller so the gas is traveling to fast for the flame to jump down the pipe to the oxygen inlet?
What does the pressures and velocities have to do with where the flame stays?
If anyone has any ideas, I'm all ears!

 

[stewartcs]

I have built a nice biomass gasifier that produces about 700,000 btu's of heat per hour by burning or flaring the gas that comes out of it.
What I want to do is, to flare the gas in an enclosed chamber so I would be able to capture all the exhaust and run it through some heat exchangers for heating hot water.
I have a suction fan that pulls the gas out of the gasifier and then blows it into the flare/burn chamber and through the heat exchangers.
In order to save using another blower to blow air, (oxygen) into the flare/burn chamber, I meter it in on the suction side of the blower where it is mixed to the correct fuel air mixture.
This works great burning the gas in the flare/burn chamber into the open atmosphere. But when I put a lid on the chamber and force the exhaust to flow through pipes to the heat exchangers, then the flare doesn't want to stay in the burn chamber. It either jumps down the pipe through the blower right to where the oxygen inlet is, or it travels up the pipes from the burn chamber towards the heat exchangers.
I would like to figure out how to get the flame to stay in the burn chamber.
Does the burn chamber need to be larger?
Does the inlet pipe need to be smaller so the gas is traveling to fast for the flame to jump down the pipe to the oxygen inlet?
What does the pressures and velocities have to do with where the flame stays?
If anyone has any ideas, I'm all ears!

If memory serves me correctly, you should be able to find some information in ANSI/API Standard 521, "Pressure-relieving and Depressurizing Systems".

That standard has a lot of information on flare stacks used in the offshore oil and gas business which sounds similar to what you are working on.

CS