Note 2 - Revenue Recognition - Revenues Disaggregated by Product Technology (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2025	Dec. 31, 2024
Revenues	$ 26,677	$ 25,133
Air Pollution Control [Member]
Revenues	8,908	11,242
Air Pollution Control [Member] \| Technology Solutions [Member]
Revenues	5,420	7,897
Air Pollution Control [Member] \| Spare Parts [Member]
Revenues	1,739	1,616
Air Pollution Control [Member] \| Ancillary Revenue [Member]
Revenues	1,749	1,729
FUEL CHEM [Member]
Revenues	17,769	13,891
FUEL CHEM [Member] \| Technology Solutions [Member]
Revenues	$ 17,769	$ 13,891

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

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+ Details