Note 2 - Revenue Recognition (Tables)

12 Months Ended

Dec. 31, 2023

Notes Tables

Disaggregation of Revenue [Table Text Block]

	Twelve Months Ended December 31,
	2023		2022
Air Pollution Control
Technology solutions	$	9,497	$	7,935
Spare parts		2,239		911
Ancillary revenue		1,747		1,751
Total Air Pollution Control technology		13,483		10,597
FUEL CHEM
FUEL CHEM technology solutions		13,598		16,344
Total Revenues	$	27,081	$	26,941

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

	Twelve Months Ended December 31,
	2023		2022
United States	$	21,062	$	20,311
Foreign Revenues
Americas		577		213
Europe		3,064		2,888
Asia		2,378		3,529
Total Foreign Revenues		6,019		6,630
Total Revenues	$	27,081	$	26,941

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

	Twelve Months Ended December 31,
	2023		2022
Products transferred at a point in time	$	17,584	$	18,849
Products and services transferred over time		9,497		8,092
Total Revenues	$	27,081	$	26,941

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

	As of
	December 31, 2023			December 31, 2022
Trade receivables	$	4,300		$	4,605
Unbilled receivables		2,285			3,082
Other short-term receivables		255			152
Allowance for credit losses		(111	)		(110	)
Total accounts receivable	$	6,729		$	7,729