Note 3 - Revenue (Tables)

9 Months Ended

Sep. 30, 2022

Notes Tables

Disaggregation of Revenue [Table Text Block]

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2022		2021		2022		2021
Air Pollution Control
Technology solutions	$	1,904	$	1,172	$	5,711	$	1,768
Spare parts		384		407		742		823
Ancillary revenue		440		365		1,217		1,246
Total Air Pollution Control technology revenues		2,728		1,944		7,670		3,837
FUEL CHEM
FUEL CHEM technology solutions		5,289		5,615		12,250		13,973
Total Revenues	$	8,017	$	7,559	$	19,920	$	17,810

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

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2022		2021		2022		2021
United States	$	6,972	$	6,049	$	14,939	$	15,100
Foreign Revenues
Latin America		56		121		185		338
Europe		613		663		1,939		1,339
Asia		376		726		2,857		1,033
Total Foreign Revenues		1,045		1,510		4,981		2,710
Total Revenues	$	8,017	$	7,559	$	19,920	$	17,810

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

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2022		2021		2022		2021
Products transferred at a point in time	$	5,969	$	6,387	$	14,065	$	16,042
Products and services transferred over time		2,048		1,172		5,855		1,768
Total Revenues	$	8,017	$	7,559	$	19,920	$	17,810

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

	As of
	September 30, 2022			December 31, 2021
Trade receivables	$	4,935		$	2,122
Unbilled receivables		1,587			1,277
Other short-term receivables		309			83
Allowance for doubtful accounts		(173	)		(223	)
Total accounts receivable	$	6,658		$	3,259