Note 3 - Revenue (Tables)

6 Months Ended

Jun. 30, 2022

Notes Tables

Disaggregation of Revenue [Table Text Block]

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2022		2021		2022		2021
Air Pollution Control
Technology solutions	$	1,966	$	223	$	3,807	$	596
Spare parts		262		236		358		416
Ancillary revenue		510		527		777		881
Total Air Pollution Control technology revenues		2,738		986		4,942		1,893
FUEL CHEM
FUEL CHEM technology solutions		3,630		4,232		6,961		8,358
Total Revenues	$	6,368	$	5,218	$	11,903	$	10,251

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

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2022		2021		2022		2021
United States	$	4,279	$	4,588	$	7,967	$	9,051
Foreign Revenues
Latin America		60		142		129		217
Europe		922		301		1,326		676
Asia		1,107		187		2,481		307
Total Foreign Revenues		2,089		630		3,936		1,200
Total Revenues	$	6,368	$	5,218	$	11,903	$	10,251

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

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2022		2021		2022		2021
Products transferred at a point in time	$	4,402	$	4,995	$	8,096	$	9,655
Products and services transferred over time		1,966		223		3,807		596
Total Revenues	$	6,368	$	5,218	$	11,903	$	10,251

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

	As of
	June 30, 2022			December 31, 2021
Trade receivables	$	5,500		$	2,122
Unbilled receivables		1,106			1,277
Other short-term receivables		78			83
Allowance for doubtful accounts		(260	)		(223	)
Total accounts receivable	$	6,424		$	3,259