Note 3 - Revenue (Tables)

9 Months Ended

Sep. 30, 2020

Notes Tables

Disaggregation of Revenue [Table Text Block]

	Three Months Ended September 30,				Nine Months Ended September 30,
	2020		2019		2020		2019
Air Pollution Control
Technology solutions	$	2,326	$	1,191	$	4,524	$	9,727
Spare parts		254		299		667		832
Ancillary revenue		306		326		828		1,849
Total Air Pollution Control Technology revenues		2,886		1,816		6,019		12,408
FUEL CHEM
FUEL CHEM technology solutions		5,269		4,636		10,315		13,147
Total Revenues	$	8,155	$	6,452	$	16,334	$	25,555

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

	Three Months Ended September 30,				Nine Months Ended September 30,
	2020		2019		2020		2019
United States	$	6,473	$	5,727	$	12,880	$	22,104
Foreign Revenues
Latin America		195		282		400		474
Europe		904		283		1,494		1,568
Asia		583		160		1,560		1,409
Total Foreign Revenues		1,682		725		3,454		3,451
Total Revenues	$	8,155	$	6,452	$	16,334	$	25,555

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

	Three Months Ended September 30,				Nine Months Ended September 30,
	2020		2019		2020		2019
Products transferred at a point in time	$	5,108	$	5,261	$	11,089	$	15,828
Products and services transferred over time		3,047		1,191		5,245		9,727
Total Revenues	$	8,155	$	6,452	$	16,334	$	25,555

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

	As of
	September 30, 2020			December 31, 2019
Trade receivables	$	4,731		$	6,425
Unbilled receivables		1,929			1,857
Other short-term receivables		29			7
Allowance for doubtful accounts		(700	)		(1,816	)
Total accounts receivable	$	5,989		$	6,473