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

12 Months Ended

Dec. 31, 2023

Notes Tables

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

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	)

For the year ended December 31, 2022	Air Pollution Control Segment			FUEL CHEM Segment			Other			Total
Revenues from external customers	$	10,597		$	16,344		$	—		$	26,941
Cost of sales		(6,924	)		(8,374	)		—			(15,298	)
Gross margin		3,673			7,970			—			11,643
Selling, general and administrative		—			—			(12,275	)		(12,275	)
Research and development		—			—			(895	)		(895	)
Operating income (loss) from continuing operations	$	3,673		$	7,970		$	(13,170	)	$	(1,527	)

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

For the years ended December 31,	2023		2022
Revenues:
United States	$	21,062	$	20,311
Foreign		6,019		6,630
	$	27,081	$	26,941

As of December 31,	2023		2022
Assets:
United States	$	46,487	$	47,007
Foreign		3,901		3,117
	$	50,388	$	50,124