Note 12 - Business Segment and Geographic Financial Data (Tables)

12 Months Ended

Dec. 31, 2025

Notes Tables

Schedule of Segment Reporting Information, by Segment [Table Text Block]

For the year ended December 31, 2025	Air Pollution Control Segment			FUEL CHEM Segment			Other			Total
Revenues from external customers	$	8,908		$	17,769		$	—		$	26,677
Cost of sales		(5,093	)		(9,201	)		—			(14,294	)
Gross margin		3,815			8,568			—			12,383
Selling, general and administrative		—			—			(14,050	)		(14,050	)
Research and development		—			—			(2,014	)		(2,014	)
Operating income (loss) from continuing operations	$	3,815		$	8,568		$	(16,064	)	$	(3,681	)

For the year ended December 31, 2024	Air Pollution Control Segment			FUEL CHEM Segment			Other			Total
Revenues from external customers	$	11,242		$	13,891		$	—		$	25,133
Cost of sales		(7,050	)		(7,460	)		—			(14,510	)
Gross margin		4,192			6,431			—			10,623
Selling, general and administrative		—			—			(13,761	)		(13,761	)
Research and development		—			—			(1,564	)		(1,564	)
Operating income (loss) from continuing operations	$	4,192		$	6,431		$	(15,325	)	$	(4,702	)

Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas [Table Text Block]

For the years ended December 31,	2025		2024
Revenues:
United States	$	21,022	$	17,802
Other Foreign		5,655		7,331
	$	26,677	$	25,133

As of December 31,	2025		2024
Assets:
United States	$	44,345	$	44,430
Foreign		2,834		4,367
	$	47,179	$	48,797