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Note 3 - Revenue (Tables)
3 Months Ended
Mar. 31, 2025
Notes Tables  
Disaggregation of Revenue [Table Text Block]
  

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

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

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

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