Control strategy 1

[maypot]

Hi,

I`m looking for an effective control strategy for a bagasse-fired boiler.

Bob

 

[Engineer6512]

Can you give us a bit more information on what you are trying to control?

Steamguy2

http://www.SteamPlantEngineering.com

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[rmw]

What is your present control strategy?

rmw

 

[maypot]

Hi,

Actually the output of the master pressure controller feeds the ID fan. The feeders are controlled by the 02 in the gas outlet and the fuel-air ratio.There is no direct interface between the master pressure and the feeding of fuel. High O2 more feed and low O2 less feed.
The combustion is kept slightly negative by a furnace pressure controller.

Bob

 

[rmw]

Does the boiler master control the speed of the fan, or a fan damper position? What does the furnace pressure controller operate in order to control negative furnace pressure, or is it as a bias or offset to the ID fan set point?

Do you have any discreet control of the FD air side, or is all combustion air flow ID Fan induced draft? If so, how is it controlled?

In another thread I alluded to OF Air. IS there any, and if so, how is it controlled?

Give some information about the feeders. (Air swept, flinger, screw fed chute???? Pin hole grates, vibrating grates???

What is your actual fuel moisture? Are you burning Bagasse right off the mill floor, or are you storing it and bringing it back in from covered or outside storage, (does it rain often on your fuel supply) or burning a blend both sources? (Goes to fuel quality/moisture variations that have to be accounted for in control systems.)

Some or all of these factors can contribute to how a boiler reacts to fuel flow/quality changes, and may have to be accounted for in any control system that someone on this board might recommend to you.

rmw

 

[maypot]

Hi rmw,

We are actually burning fuel with a very high content of CO > 10000 ppm. This means that the combustion is rather incomplete but the O2 in the flue gas is only around 2 % . By pushing more air , the pressure in the combustion chamber becomes more positive( > 50 Pa ) killing the fire instead. I believe that the ID is not capable to provide the negative draft at a particular load. Can I conclude that the ID is underrated ? But I am being told that the boiler was delivering the load in the past.
If the boiler is sucking air between the gas oulet and the economiser outlet,which I believe is true becuase the O2 after the economiser is 4-5 %,could it reduce the efficiency of the ID ?
How can I determine the capacity of the ID for a particular load ? The ID fan controller is most of the times at 100 %/

Bob

 

[rmw]

Sorry I did not see your last reply in this thread until now. I have had a heavy travel schedule and haven't been to the site on a regular basis for a couple of weeks now.

I think my answer in thread794-132511 referring to an earlier answer is what you are looking for. Any leakage that the fan has to handle robs the fan of capacity that could be used for pulling air through the furnace contributing to the combustion and draft control.

rmw