Revenue (Tables)

3 Months Ended

Mar. 31, 2020

Revenue from Contract with Customer [Abstract]

Disaggregation of Revenue

The following table presents the timing of our revenue recognition:

	Three Months Ended   March 31,
	2020		2019
Products transferred at a point in time	$	3,049	$	5,414
Products and services transferred over time	729		4,741
Total Revenues	$	3,778	$	10,155

The following table presents our revenues disaggregated by product technology:

	Three Months Ended   March 31,
	2020		2019
Air Pollution Control
Technology solutions	$	729	$	4,741
Spare parts	199		149
Ancillary revenue	268		899
Total Air Pollution Control Technology revenues	1,196		5,789
FUEL CHEM
FUEL CHEM technology solutions	2,582		4,366
Total Revenues	$	3,778	$	10,155

Revenue Disaggregated by Geography

The following table presents our revenues disaggregated by geography, based on the billing addresses of our customers:

	Three Months Ended   March 31,
	2020		2019
United States	$	3,097	$	8,815
Foreign Revenues
Latin America	146		175
Europe	393		617
Asia	142		548
Total Foreign Revenues	681		1,340
Total Revenues	$	3,778	$	10,155

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

The components of accounts receivable are as follows:

	As of
	March 31, 2020			December 31, 2019
Trade receivables	$	5,496		$	6,425
Unbilled receivables	1,886			1,857
Other short-term receivables	33			7
Allowance for doubtful accounts	(1,795		)	(1,816		)
Total accounts receivable	$	5,620		$	6,473