Why Is Our Biomass Boiler Underperforming?

[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.

 

[eljose79]

Thank you for reaching out to the scientific community for help with your biomass boiler issue. I would like to offer some potential explanations for the strange behavior of your boiler.

Firstly, it is important to note that the laws of physics are universal and cannot be defied. However, there may be some factors at play that are causing the boiler to behave differently than expected.

One possibility is that there may be a malfunction or blockage in the heat exchanger, causing a decrease in heat transfer efficiency. This could explain the low delta T flow/return and the lower water temperature being produced. I would suggest checking the heat exchanger for any build-up or damage that may be hindering its performance.

Another factor to consider is the air handling units and door curtains that are connected to the boiler. If these units are not functioning properly or are not receiving enough hot water from the boiler, it could be causing the boiler to work harder to maintain the set temperature. I would recommend checking the three port valves and heat exchangers for any issues that may be affecting their performance.

It is also possible that there may be an issue with the primary and secondary pump speeds. Even though they are set to the original design parameters, it is possible that they may have shifted or malfunctioned, causing the boiler to work harder to deliver the required amount of heat. I would suggest double-checking these parameters and potentially adjusting them if necessary.

Overall, it seems that the energy is not being lost, but rather not being efficiently transferred to the water. I would recommend checking all components of the system for any issues that may be causing this decrease in efficiency. If necessary, it may be helpful to consult with a professional technician or engineer who specializes in biomass boilers to further troubleshoot the issue.

I hope this information helps and I wish you the best of luck in resolving the issue with your boiler.