Moisture measurement on a bagasse boiler

[Delfos]

I have a 250HP bagasse boiler and I'm interested on installing a moisture transmitter to compensate moisture changes that usually are between 40% to 50%. We have a lot of bagasse so fuel efficiency is not an issue. Some people have told me that it would help me to keep constant pressure on load changes.

Also, we are installing a combustion lead-lag parallel-series with demand control and maybe an oxygen trim. This would be enough?

It's worth the investment on a moisture transmitter for this case?

 

[rmw]

What would you control with the output of this moisture meter? If the moisture content varied over a wider range, I might could see it, but not for that little difference.

What is making your bagasse moisture vary? Are you varying your imbibition water? Why not try to tighten up on that? Are you varying your grinding speed? Are you mixing dryer fuel with storage with bagasse coming straight off the grinding floor? I would look at what is making your moisture content vary.

Bagasse as with any solid fuel that is ~40-60% moisture has to be dried out before it can begin to be combusted. When your boiler senses a load demand change (increase) it adds fuel which dumps wet fuel into the furnace. That puts an additional load on the boiler, first trying to meet the load increase demand, and second, having to dry the additional fuel.

The secret is slowing down the rate of increase of the fuel addition so that it doesn't quench the fire in the furnace by dumping a lot of wet bagasse on the grates.

Do you have an air preheater on the boiler. If not, now that is an investment worth making. Bringing in 400F degree combustion air helps with the bagasse drying and combustion.

I am a big fan of O2 trim control.... except maybe in the case of bark and bagasse fired boilers. With the problem mentioned above regarding drying and combusting the fuel, there is the need to have good air penetration above the grates for complete combustion; the burning of the solid particles as the volatiles burn off and they get light. If the air is pinched back too much by O2 trim control, this can lead to incomplete combustion of the fuel and a lot of char carryover.

Let us know what you decide.

rmw