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

12 Months Ended

Dec. 31, 2024

Notes Tables

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

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	)

For the year ended December 31, 2023	Air Pollution Control Segment			FUEL CHEM Segment			Other			Total
Revenues from external customers	$	13,483		$	13,598		$	—		$	27,081
Cost of sales		(8,410	)		(7,015	)		—			(15,425	)
Gross margin		5,073			6,583			—			11,656
Selling, general and administrative		—			—			(12,803	)		(12,803	)
Research and development		—			—			(1,511	)		(1,511	)
Operating income (loss) from continuing operations	$	5,073		$	6,583		$	(14,314	)	$	(2,658	)

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

For the years ended December 31,	2024		2023
Revenues:
United States	$	17,802	$	21,397
Other Foreign		7,331		5,684
	$	25,133	$	27,081

As of December 31,	2024		2023
Assets:
United States	$	44,430	$	46,487
Foreign		4,367		3,901
	$	48,797	$	50,388