Note 3 - Revenue (Tables)

6 Months Ended

Jun. 30, 2024

Notes Tables

Disaggregation of Revenue [Table Text Block]

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2024		2023		2024		2023
Air Pollution Control
Technology solutions	$	2,619	$	2,557	$	4,283	$	5,539
Spare parts		805		425		1,004		599
Ancillary revenue		525		440		980		843
Total Air Pollution Control technology revenues		3,949		3,422		6,267		6,981
FUEL CHEM
FUEL CHEM technology solutions		3,093		2,039		5,732		5,767
Total Revenues	$	7,042	$	5,461	$	11,999	$	12,748

Revenue from External Customers by Geographic Areas [Table Text Block]

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2024		2023		2024		2023
United States	$	4,471	$	4,316	$	8,066	$	10,297
Foreign Revenues
Latin America		293		153		608		153
Europe		1,688		820		2,544		1,399
Asia		590		172		781		899
Total Foreign Revenues		2,571		1,145		3,933		2,451
Total Revenues	$	7,042	$	5,461	$	11,999	$	12,748

Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table Text Block]

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2024		2023		2024		2023
Products transferred at a point in time	$	4,423	$	2,904	$	7,716	$	7,209
Products and services transferred over time		2,619		2,557		4,283		5,539
Total Revenues	$	7,042	$	5,461	$	11,999	$	12,748

Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block]

	As of
	June 30, 2024			December 31, 2023
Trade receivables	$	5,182		$	4,300
Unbilled receivables		1,543			2,285
Receivable for employee retention credit		1,677			—
Other short-term receivables		355			255
Allowance for credit losses		(106	)		(111	)
Total accounts receivable	$	8,651		$	6,729