Note 3 - Revenue (Tables)

3 Months Ended

Mar. 31, 2024

Notes Tables

Disaggregation of Revenue [Table Text Block]

	Three Months Ended
	March 31,
	2024		2023
Air Pollution Control
Technology solutions	$	1,664	$	2,982
Spare parts		199		174
Ancillary revenue		455		403
Total Air Pollution Control technology revenues		2,318		3,559
FUEL CHEM
FUEL CHEM technology solutions		2,639		3,728
Total Revenues	$	4,957	$	7,287

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

	Three Months Ended
	March 31,
	2024		2023
United States	$	3,595	$	5,981
Foreign Revenues
Latin America		315		—
Europe		856		579
Asia		191		727
Total Foreign Revenues		1,362		1,306
Total Revenues	$	4,957	$	7,287

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

	Three Months Ended
	March 31,
	2024		2023
Products transferred at a point in time	$	3,293	$	4,305
Products and services transferred over time		1,664		2,982
Total Revenues	$	4,957	$	7,287

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

	As of
	March 31, 2024			December 31, 2023
Trade receivables	$	3,769		$	4,300
Unbilled receivables		1,507			2,285
Receivable for employee retention credit		1,677			—
Other short-term receivables		262			255
Allowance for credit losses		(111	)		(111	)
Total accounts receivable	$	7,104		$	6,729