Note 3 - Revenue

9 Months Ended

Sep. 30, 2025

Notes to Financial Statements

Revenue from Contract with Customer [Text Block]

3.     Revenue

Disaggregated Revenue by Product Technology

The following table presents our revenues disaggregated by product technology:

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2025		2024		2025		2024
Air Pollution Control
Technology solutions	$	1,227	$	2,554	$	3,443	$	6,837
Spare parts		840		424		1,516		1,428
Ancillary revenue		640		246		1,556		1,226
Total Air Pollution Control technology revenues		2,707		3,224		6,515		9,491
FUEL CHEM
FUEL CHEM technology solutions		4,783		4,627		12,915		10,359
Total Revenues	$	7,490	$	7,851	$	19,430	$	19,850

Disaggregated Revenue by Geography

The following table presents our revenues disaggregated by geography, based on the location of the end-user:

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2025		2024		2025		2024
United States	$	5,626	$	5,453	$	15,427	$	13,519
Foreign Revenues
Latin America		166		208		579		816
Europe		698		785		1,882		1,627
Africa		68		741		262		2,443
Asia		932		664		1,280		1,445
Total Foreign Revenues		1,864		2,398		4,003		6,331
Total Revenues	$	7,490	$	7,851	$	19,430	$	19,850

Timing of Revenue Recognition

The following table presents the timing of our revenue recognition:

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2025		2024		2025		2024
Products transferred at a point in time	$	6,263	$	5,297	$	15,987	$	13,013
Products and services transferred over time		1,227		2,554		3,443		6,837
Total Revenues	$	7,490	$	7,851	$	19,430	$	19,850

Contract Balances

The timing of revenue recognition, billings, and cash collections results in billed accounts receivable, unbilled receivables (contract assets), and customer advances and deposits (contract liabilities) on the Condensed Consolidated Balance Sheets. In our Air Pollution Control (APC) technology segment, amounts are billed as work progresses in accordance with agreed-upon contractual terms. Generally, billing occurs subsequent to revenue recognition, resulting in contract assets. These assets are reported on the Condensed Consolidated Balance Sheets on a contract-by-contract basis at the end of each reporting period. At September 30, 2025,  December 31, 2024, and December 31, 2023, contract assets for APC technology projects were approximately $1,300, $2,075, and $2,285, respectively. 

The Company will periodically bill in advance of costs incurred before revenue is recognized, resulting in contract liabilities. These liabilities are reported on the Condensed Consolidated Balance Sheets on a contract-by-contract basis at the end of each reporting period. Contract liabilities were $2,200, $721, and $1,279 at September 30, 2025,  December 31, 2024, and December 31, 2023, respectively, and are included in other accrued liabilities on the Condensed Consolidated Balance Sheets.

Changes in the contract asset and liability balances during the nine-month period ended September 30, 2025 were not materially impacted by any other items other than amounts billed and revenue recognized as described previously. Revenue recognized that was included in the contract liability balance at the beginning of the period was $1 and $544 for the three and nine months ended September 30, 2025, respectively, and $20 and $1,241 for the three and nine months ended September 30, 2024, respectively, which represented revenue from progress towards completion of our APC technology contracts.

As of September 30, 2025 and December 31, 2024, we had no construction contracts in progress that were identified as a loss contract. 

Remaining Performance Obligations

Remaining performance obligations represents the transaction price of APC technology booked orders for which work has not been performed. As of September 30, 2025, the aggregate amount of the transaction price allocated to remaining performance obligations was $9,472. The Company expects to recognize revenue on approximately $7,134 of the remaining performance obligations over the next 12 months with the remaining recognized thereafter. 

Accounts Receivable

The components of accounts receivable are as follows:

	As of
	September 30, 2025			December 31, 2024
Trade receivables	$	3,315		$	5,375
Unbilled receivables		1,300			2,075
Receivable for employee retention credit		—			1,677
Other short-term receivables		321			347
Allowance for credit losses		(108	)		(106	)
Total accounts receivable	$	4,828		$	9,368