Note 3 - Revenue (Tables)

6 Months Ended

Jun. 30, 2023

Notes Tables

Disaggregation of Revenue [Table Text Block]

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2023		2022		2023		2022
Air Pollution Control
Technology solutions	$	2,557	$	1,966	$	5,539	$	3,807
Spare parts		425		262		599		358
Ancillary revenue		440		510		843		777
Total Air Pollution Control technology revenues		3,422		2,738		6,981		4,942
FUEL CHEM
FUEL CHEM technology solutions		2,039		3,630		5,767		6,961
Total Revenues	$	5,461	$	6,368	$	12,748	$	11,903

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

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2023		2022		2023		2022
United States	$	4,316	$	4,279	$	10,297	$	7,967
Foreign Revenues
Latin America		153		60		153		129
Europe		820		922		1,399		1,326
Asia		172		1,107		899		2,481
Total Foreign Revenues		1,145		2,089		2,451		3,936
Total Revenues	$	5,461	$	6,368	$	12,748	$	11,903

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

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2023		2022		2023		2022
Products transferred at a point in time	$	2,904	$	4,402	$	7,209	$	8,096
Products and services transferred over time		2,557		1,966		5,539		3,807
Total Revenues	$	5,461	$	6,368	$	12,748	$	11,903

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

	As of
	June 30, 2023			December 31, 2022
Trade receivables	$	3,804		$	4,605
Unbilled receivables		2,946			3,082
Other short-term receivables		141			152
Allowance for credit losses		(110	)		(110	)
Total accounts receivable	$	6,781		$	7,729