Note 2 - Revenue Recognition - Revenues Disaggregated by Product Technology (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2024	Dec. 31, 2023
Revenues	$ 25,133	$ 27,081
Air Pollution Control [Member]
Revenues	11,242	13,483
Air Pollution Control [Member] \| Technology Solutions [Member]
Revenues	7,897	9,497
Air Pollution Control [Member] \| Spare Parts [Member]
Revenues	1,616	2,239
Air Pollution Control [Member] \| Ancillary Revenue [Member]
Revenues	1,729	1,747
FUEL CHEM [Member]
Revenues	13,891	13,598
FUEL CHEM [Member] \| Technology Solutions [Member]
Revenues	$ 13,891	$ 13,598

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