Where has all that energy gone to?

[vespak]

I am not a physicist however I am hoping some of you can help me out. We run biomass boilers in big supermarket stores so that they can appease the carbon levy and build ever more of them! One such boiler is behaving very strangely and defying all the laws of physics of my limited understanding. The boiler is running flat out in its boost mode trying to attain a set point of 78ºC. It has a furnace temperature of 700ºC which being a small 750kW boiler means this is the heat being transported directly through the heat exchanger. (water jacket surrounding a series of tubes through which the flue gas passes twice - 50% through the lower set and then reverses 50% through the upper set) The flue gas temperature (measured 500mm after the gas exits the heat exchanger) is 158ºC therefore the boiler is delivering 542ºC +/- to the heat exchanger.
The delta T flow/return is only 1.8ºC and the boiler is only managing to produce a water temperature of max 62ºC. Prior to the last few days it has achieved its normal set point without having to run it flat out at a normal delta t 10ºC+/-.
There is no back end three port valve on this system so its not blending the return and we have checked the primary and secondary pump speeds, they are as the original design parameters. The boiler is supplying 3 air handling units and approx 6 door curtains all of which have three port valves and heat exchangers.
Any one got any idea as to what's going on? where is all this energy going to.
All advice gratefully received.

 

[Studiot]

Flow rate?

Partial blockage?

 

[lorrad]

There is a blockage somewhere within the boiler itself .. not a cheap fix

while not a total blockage .. the water is probably boiling before the blockage and condensing after the blockage releasing energy back into the system and reducing the temperature of the water output.

what would cause the blockage .. a structural failure point that was in the boiler at manufacture most likely. It just took a while to show up.

I am not a physicist either I am a repair person albeit retired, but that is the place I would first look.

 

[Jobrag]

Have you checked the relief valve, if that is passing you could be loosing hot water down the drain.

 

[vespak]

Thanks for all your reply's our best guess at the moment is a small leak in the HX. There would be no evident water as it would vaporize in the flue gas. Will update after we investigate tomorrow.