Note 3 - Revenue (Tables)

9 Months Ended

Sep. 30, 2023

Notes Tables

Disaggregation of Revenue [Table Text Block]

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2023		2022		2023		2022
Air Pollution Control
Technology solutions	$	1,910	$	1,904	$	7,449	$	5,711
Spare parts		1,339		384		1,938		742
Ancillary revenue		462		440		1,305		1,217
Total Air Pollution Control technology revenues		3,711		2,728		10,692		7,670
FUEL CHEM
FUEL CHEM technology solutions		4,277		5,289		10,044		12,250
Total Revenues	$	7,988	$	8,017	$	20,736	$	19,920

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

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2023		2022		2023		2022
United States	$	5,640	$	6,972	$	15,937	$	14,939
Foreign Revenues
Latin America		157		56		310		185
Europe		1,001		613		2,400		1,939
Asia		1,190		376		2,089		2,857
Total Foreign Revenues		2,348		1,045		4,799		4,981
Total Revenues	$	7,988	$	8,017	$	20,736	$	19,920

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

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2023		2022		2023		2022
Products transferred at a point in time	$	6,078	$	5,969	$	13,287	$	14,065
Products and services transferred over time		1,910		2,048		7,449		5,855
Total Revenues	$	7,988	$	8,017	$	20,736	$	19,920

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

	As of
	September 30, 2023			December 31, 2022
Trade receivables	$	5,717		$	4,605
Unbilled receivables		1,944			3,082
Other short-term receivables		145			152
Allowance for credit losses		(110	)		(110	)
Total accounts receivable	$	7,696		$	7,729