biomass boiler furnace temperature

[dave7840]

After some advice about furnace temperatures, we had a new boiler installed in January to dry woodchip. the boiler is rated at 950kw but the average the installer can get out of it is 750kw. they are basically blaming everything on the fuel. first it was to wet, then to dry, then to much fines, if they can think of it, its that, not the boiler. i do know thats always the first thing they blame we have 3 other different make smaller boilers. i have been trying lots of different settings aswell but i think the limiting factor is the furnace temp. its currently set at max 850c .if i try to push more fuel in, the egr will limit the temp and the fuel ends up burning too far up the grates. so we have run some trials today at different furnace temps to see if made any difference and it made a massive change we ran for 4 hours at 900c averaged 840kw and 950c averaged 930kw. what im asking is what temp should or could we run it at? just for reference i know lower is better the other boilers all run at 600c

 

[f0ster]

the egr is there to protect the boiler and prolong the life of the boiler combustion chamber parts, you might find you are having to replace the concrete lining more often, monitor the flue gas temp, this will be a good indication of how efficient the heat exchanger is, and possibly by how much you are going to shorten the life of the boiler. we were looking after a 350kw eta that had a chamber temp of 950 deg and a flue gas temp of well under 150 deg, the egr kicked in at 950 deg, I thought it was a bit high but eta tec said it was ok.

 

[Doing it for the kids]

Interesting questions.

May I ask what boiler this is?

what size flow and return stubs came on the boiler and what sized pipes did they plumb to it (did they step them down)

often plumbers skimp here but I suspect this may not be the case with yours?

 

[dave7840]

the flue gas temp was about 145 to 150 when on 850c but is now upto 155 to 160 at 950c.
the boiler is a kal vis (ive split it so google search hopeful wont pick it up)
the pipe work is all about 100mm, there are no step downs between the stubs and pipe work

 

[Doing it for the kids]

not sure on flue temps, others will though.

100mm seems small for that size, ive 3 inch on a 200 kwh unit and 4 inch on a 650. I fitted 5 to 950.

 

[dave7840]

it could bigger ive never measured them. i dont think thats the problem though because with it set at 850c the flow temp would be around 80c even though its set at 87c, so the boiler is never keeping up with demand

 

[rollestonpark]

I've done a fair bit of experimenting with my Froling boiler on class A waste wood. I was told it was set as best as it could be (TM250) doing 200kw. The fuel is crap. etc etc.
After messing with the settings and getting a better understanding of burning, I now realise that the 'its rubbish fuel' is complete tosh. (unless very wet of course)

Either the boiler is not set right or the boiler was never built to do what it says on the label.
Certain brands I could mention only do what the label says when completely clean and on pellets or perfect fuel.
Frolings normally do what they say and often more when pushed.

My TM250 will do 300kw on waste wood when clean and pushed, 250kw when dirty (8+ months without cleaning etc)

On my boiler to push it, these are the things:
Get flue gas temperatures to 150c or more maybe upto 180c
To keep the chamber temperature down but still get the output (with this v dry waste wood) double the FGR fan speed from the factory setting.
Increase the secondary air if the chamber is still too hot ie 1000c or more, (frolings back the fuel rate off at 1000c to protect themselves)
Increase fuel input rate, but more fuel means more air, more draft.
Run more primary if the chamber too cold and set FGR back to standard or lower.
Sometimes need to make grate move more frequently if the fuel isn't burning all the way along the grate irons (we need that chamber full of burning fuel and ash only just as it's about to fall off the end)
Sometimes you need to increase the draft fan to drag the hot gases higher up into the heat exchanger. To get the output.

Also on the Frolings the ash augers that remove ash from the heat exchanger need to run twice as much as factory when burning dusty class A waste wood fuels, and double the heat exchanger cleaning rate.
This is because large amounts of fines (with my waste wood) get burned quickly and lift off into the gases and fill the heat exchanger quicker. So they must be removed more aggressively.

Some ideas that you might want to try.
The frolings have a graphing program so you can see the historical data on a graph for the last 24+ hours, this helps a lot in setting up the boiler to it's max, maybe your supplier has something like this?

Chris

 

[dave7840]

thanks for your detailed reply. there are some points we have tried and others we haven't, so will try them. first jobs today are to rip out the ash chain and slat because the links are always seizing and to make up a bin that will fit the pit, then to swap out the motor on the fuel feed rotary tank because it keeps tripping out and is off again now. oh the joys of running biomass boilers

 

[rollestonpark]

Oh dear, does sound like your struggling with it. Not really had any hassle with my Froling boiler. Thank god.
Let us know, how you get on with the settings.

Good luck

 

[A1an]

Ive never been a fan of running our boilers flat out. Its a big investment, you want them to last with minimal maintenance costs.