Note 14 - Business Segment, Geographic and Quarterly Financial Data (Tables)

12 Months Ended

Dec. 31, 2020

Notes Tables

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

For the year ended December 31, 2020	Air Pollution Control Segment			FUEL CHEM Segment			Other			Total
Revenues from external customers	$	8,557		$	13,993		$	—		$	22,550
Cost of sales		(4,583	)		(7,329	)		—			(11,912	)
Gross margin		3,974			6,664			—			10,638
Selling, general and administrative		—			—			(13,600	)		(13,600	)
Restructuring charge		—			—			—			—
Research and development		—			—			(1,177	)		(1,177	)
Intangible assets abandonment		—			—			(197	)		(197	)
Operating income (loss) from continuing operations	$	3,974		$	6,664		$	(14,974	)	$	(4,336	)

For the year ended December 31, 2019	Air Pollution Control Segment			FUEL CHEM Segment			Other			Total
Revenues from external customers	$	14,082		$	16,385		$	—		$	30,467
Cost of sales		(11,256	)		(8,381	)		—			(19,637	)
Gross margin		2,826			8,004			—			10,830
Selling, general and administrative		—			—			(17,191	)		(17,191	)
Restructuring charge		(625	)		—			—			(625	)
Research and development		—			—			(1,127	)		(1,127	)
Intangible assets abandonment		—			—			(127	)		(127	)
Operating income (loss) from continuing operations	$	2,201		$	8,004		$	(18,445	)	$	(8,240	)

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

For the years ended December 31,	2020		2019
Revenues:
United States	$	18,622	$	25,882
Foreign		3,928		4,585
	$	22,550	$	30,467

As of December 31,	2020		2019
Assets:
United States	$	24,524	$	23,460
Foreign		5,564		8,764
	$	30,088	$	32,224