Note 2 - Revenue Recognition (Tables)

12 Months Ended

Dec. 31, 2024

Notes Tables

Disaggregation of Revenue [Table Text Block]

	Twelve Months Ended December 31,
	2024		2023
Air Pollution Control
Technology solutions	$	7,897	$	9,497
Spare parts		1,616		2,239
Ancillary revenue		1,729		1,747
Total Air Pollution Control technology		11,242		13,483
FUEL CHEM
FUEL CHEM technology solutions		13,891		13,598
Total Revenues	$	25,133	$	27,081

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

	Twelve Months Ended December 31,
	2024		2023
United States	$	17,802	$	21,397
Foreign Revenues
Americas		924		577
Europe		2,146		2,558
South Africa		2,570		163
Pacific Rim and other		1,691		2,386
Total Foreign Revenues		7,331		5,684
Total Revenues	$	25,133	$	27,081

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

	Twelve Months Ended December 31,
	2024		2023
Products transferred at a point in time	$	17,236	$	17,584
Products and services transferred over time		7,897		9,497
Total Revenues	$	25,133	$	27,081

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

	As of
	December 31, 2024			December 31, 2023
Trade receivables	$	5,375		$	4,300
Unbilled receivables		2,075			2,285
Receivable for employee retention credit		1,677			—
Other short-term receivables		347			255
Allowance for credit losses		(106	)		(111	)
Total accounts receivable	$	9,368		$	6,729