Welcome Ori.
My much better half is a glassblower and engraver. I know the dilemma you describe.
The answer is manifold, but I agree that function stacking is key to offsetting the energy expenditure.
As to burning biomass, while I think it's possible, I have been told that not only would a great deal of biomass would be required, but that even with optimal burn conditions, particulates and contaminants in the furnace environment would dirty the glass.
To that end, and that of carbon capture, storage, and soil-building, I would consider large-scale gasification of biomass. Ultimately, even a system that used propane conventionally upon startup, then used the exhaust to pyrolise biomass into charcoal for the making of
biochar, burning the offgassed volatiles as fuel would be of greater benefit to the system as a whole. The fuel for the secondary process of pyrolisis that provides the
wood gas or equivalent and creates the biochar-to-be would otherwise go straight up the chimney.
I would make the end of any reuse loop an exhaust manifold that offered up its heat and carbon dioxide to a
greenhouse environment.
Ultimately, for larger operations, a
solar thermal array that tracks the sun, as recently popularised by a Bill Gates-sponsored company but having existed in cruder form for decades, can, in certain environments, maintain glass furnace temperatures directly. I think that a homestead-scale system, though cruder, could still be fashioned to operate a shipping-container-sized
solar pyroliser that would provide woodgas/biomassgas for many homestead functions.
I think that trapping and keeping the heat in the furnace would be of prime concern. I mean, you want the glass furnace to stay hot on its own without adding heat for as long as you can physically make it. Heat stress is what kills all glass furnace components, and that's not extended durations of time at high temperatures, but the expansion and contraction caused by heating and cooling, exacerbated by rapidity. We essentially want these things to be RMH-masonry-unit-haybox cookers, with the furnace itself and the gloryhole being your black ovens, and your annealer being your variable-temperature white or clean
oven.
Thinking out of the box, were one living on melting permafrost, where methane is offgassing freely, if one were able to cover a thawing area with one of those inflatable sports domes, well it would be necessary to know the average rate of offgassing for the given area, but such a methane capture tent could theoretically provide a stream of biogas one could filter for clean burning within a glass furnace environment, and the conversion of methane to heat and carbon dioxide is better by far in the short-term, methane being 20 times more effective a
greenhouse gas than carbon dioxide.
Alternately, if one were on
land that had extant natural gas
wells, that might be the most energy and carbon-efficient means of doing what you're doing. I would simply start thinking about it in terms of an exchange of fossil carbon for biochar whose feedstock is grown faster and more abundantly due to constant application of biochar.
Lastly, I was thinking about a thermal battery along the lines of the molten salt portion of molten salt reactors. If you have an insulated "well" or buried insulated vessel filled with a substance that can hold a great deal of heat, it can be used over time to heat
water, make steam, and operate refrigeration cycles, among other things. This might be the simplest solution by far for reclaiming the exhaust heat in a useable form from a conventional process, or as a module of any greater process.
I am looking forward to even such a challenge as trying to make use of the exhaust heat of a propane or natural gas-fuelled conventional furnace to make charcoal, but anything we can do to use more of that energy is worthwhile.
Keep us posted, and good luck.
-CK
A human being should be able to change a diaper, plan an invasion, butcher a hog, conn a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly. Specialization is for insects.
-Robert A. Heinlein