Note 3 - Revenue

3 Months Ended

Mar. 31, 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
	March 31,
	2025		2024
Air Pollution Control
Technology solutions	$	571	$	1,664
Spare parts		251		199
Ancillary revenue		481		455
Total Air Pollution Control technology revenues		1,303		2,318
FUEL CHEM
FUEL CHEM technology solutions		5,079		2,639
Total Revenues	$	6,382	$	4,957

Disaggregated Revenue by Geography

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

	Three Months Ended
	March 31,
	2025		2024
United States	$	5,359	$	3,595
Foreign Revenues
Latin America		348		315
Europe		477		420
Africa		38		436
Asia		160		191
Total Foreign Revenues		1,023		1,362
Total Revenues	$	6,382	$	4,957

Timing of Revenue Recognition

The following table presents the timing of our revenue recognition:

	Three Months Ended
	March 31,
	2025		2024
Products transferred at a point in time	$	5,811	$	3,293
Products and services transferred over time		571		1,664
Total Revenues	$	6,382	$	4,957

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 March 31, 2025,  December 31, 2024, and December 31, 2023, contract assets for APC technology projects were approximately $572, $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 $627, $721, and $1,279 at March 31, 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 three-month period ended March 31, 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 $372 and $1,121 for the three months ended March 31, 2025 and 2024, respectively, which represented revenue from progress towards completion of our APC technology contracts.

As of March 31, 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 March 31, 2025, the aggregate amount of the transaction price allocated to remaining performance obligations was $10,328. The Company expects to recognize revenue on approximately $6,924 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
	March 31, 2025			December 31, 2024
Trade receivables	$	3,087		$	5,375
Unbilled receivables		572			2,075
Receivable for employee retention credit		1,677			1,677
Other short-term receivables		405			347
Allowance for credit losses		(106	)		(106	)
Total accounts receivable	$	5,635		$	9,368