Note 3 - Revenue (Tables)

3 Months Ended

Mar. 31, 2023

Notes Tables

Disaggregation of Revenue [Table Text Block]

	Three Months Ended
	March 31,
	2023		2022
Air Pollution Control
Technology solutions	$	2,982	$	1,841
Spare parts		174		96
Ancillary revenue		403		267
Total Air Pollution Control technology revenues		3,559		2,204
FUEL CHEM
FUEL CHEM technology solutions		3,728		3,331
Total Revenues	$	7,287	$	5,535

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

	Three Months Ended
	March 31,
	2023		2022
United States	$	5,981	$	3,688
Foreign Revenues
Latin America		—		69
Europe		579		404
Asia		727		1,374
Total Foreign Revenues		1,306		1,847
Total Revenues	$	7,287	$	5,535

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

	Three Months Ended
	March 31,
	2023		2022
Products transferred at a point in time	$	4,305	$	3,694
Products and services transferred over time		2,982		1,841
Total Revenues	$	7,287	$	5,535

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

	As of
	March 31, 2023			December 31, 2022
Trade receivables	$	3,295		$	4,605
Unbilled receivables		3,444			3,082
Other short-term receivables		126			152
Allowance for credit losses		(110	)		(110	)
Total accounts receivable	$	6,755		$	7,729