FTEK Fuel Tech Inc

Organization, Consolidation and Presentation of Financial Statements Disclosure and Significant Accounting Policies [Text Block]

1. ORGANIZATION AND SIGNIFICANT ACCOUNTING POLICIES

Organization

Basis of Presentation

The consolidated financial statements include the accounts of Fuel Tech and its wholly owned subsidiaries.

Geopolitical and Unexpected Events

Liquidity

Use of Estimates

Fair Value Measurements

The carrying values of cash and cash equivalents, accounts receivable, and accounts payable are reasonable estimates of their fair value due to their short-term nature.

•

Level 1 – Observable inputs to the valuation methodology such as quoted prices in active markets for identical assets or liabilities

•

Cash and cash equivalents

	December 31, 2023		December 31, 2022
Cash	$	12,495	$	12,560
Cash equivalents		5,083		10,768
Total cash and cash equivalents shown in the Consolidated Statements of Cash Flows	$	17,578	$	23,328

Investments

The following table provides the amortized cost, gross unrealized gains and losses, and fair value of our HTM debt securities:

	December 31,
	2023			2022
Held-to-maturity debt securities:
Amortized cost	$	15,800		$	9,341
Gross unrecognized gains		—			—
Gross unrecognized losses		(86	)		(168	)
Fair value	$	15,714		$	9,173

The following table provides the amortized cost and fair value of debt securities by maturities at December 31, 2023:

	Amortized Cost		Fair Value
Within one year	$	12,136	$	12,056
After one year through two years		3,664		3,658
Total	$	15,800	$	15,714

Foreign Currency Risk Management

Accounts Receivable

Allowance for Credit Losses

Year	Balance at January 1		Provision charged to expense			Write-offs / Recoveries			Balance at December 31
2022	$	223	$	(19	)	$	(94	)	$	110
2023	$	110	$	24		$	(23	)	$	111

Prepaid expenses and other current assets

Prepaid expenses and other current assets are short-term commitments of typically three to six months for future payments and can be redeemed at a discount or applied to future vendor payments.

Inventories

Inventories consist primarily of equipment constructed for resale and spare parts and are stated at the lower of cost or net realizable value, using the weighted-average cost method. At December 31, 2023 and 2022, inventory included equipment constructed for resale of$207 and $207, respectively, and spare parts, net of reserves of $232 and $185, respectively. Usage is recorded in cost of sales in the period that parts were issued to a project, used to service equipment, or sold to customers. Equipment constructed for resale that is in process is recorded in Other assets. In process equipment for inventory recorded as other assets was $618 and $634 as of December 31, 2023 and 2022, respectively.

Year	Balance at January 1		Provision charged to expense			Write-offs / Recoveries			Balance at December 31
2022	$	927	$	—		$	—		$	927
2023	$	927	$	(56	)	$	(258	)	$	613

Foreign Currency Translation and Transactions

Accumulated Other Comprehensive Loss

	December 31,
	2023			2022
Foreign currency translation
Balance at beginning of period	$	(1,728	)	$	(1,604	)
Other comprehensive loss:
Foreign currency translation adjustments (1)		(20	)		(124	)
Balance at end of period	$	(1,748	)	$	(1,728	)
Total accumulated other comprehensive loss	$	(1,748	)	$	(1,728	)

(1)	In all periods presented, there were no tax impacts related to functional currency translation adjustments.

Research and Development

Product/System Warranty

Goodwill

Other Intangible Assets

During the years ended December 31, 2023 and 2022, Fuel Tech recorded no patent or trademark abandonment charges.

			2023							2022
Description of Other Intangibles	Amortization Period (years)		Gross Carrying Amount		Accumulated Amortization			Net Carrying Amount		Gross Carrying Amount		Accumulated Amortization			Net Carrying Amount
Patent assets		1 - 20		826		(468	)		358		803		(406	)		397
Total			$	826	$	(468	)	$	358	$	803	$	(406	)	$	397

The table below shows the estimated future amortization expense for intangible assets:

Year	Estimated Amortization Expense
2024	$	54
2025		33
2026		32
2027		32
2028		32
Thereafter		175
Total	$	358

Property and Equipment

Description of Property and Equipment	Depreciable Life (years)		2023			2022
Land			$	1,050		$	1,050
Building		39		3,950			3,950
Building and leasehold improvements		3 - 39		2,655			2,626
Field equipment		3 - 4		12,100			11,882
Computer equipment and software		2 - 3		2,049			2,117
Furniture and fixtures		3 - 10		1,307			1,306
Vehicles		5		32			32
Construction in process				99			29
Total cost				23,242			22,992
Less accumulated depreciation				(18,703	)		(18,557	)
Total net book value			$	4,539		$	4,435

Revenue Recognition

The Company recognizes revenue when control of the promised goods or services is transferred to our customers, in an amount that reflects the consideration we expect to be entitled to in exchange for those goods or services. The majority of our contracts have a single performance obligation as the promise to transfer the individual goods or services is not separately identifiable from other promises in the contracts and, therefore, not distinct. Revenue is measured as the amount of consideration we expect to receive in exchange for transferring goods or providing services. Sales, value add, and other taxes we collect concurrent with revenue-producing activities are excluded from revenue.

Air Pollution Control Technology

FUEL CHEM

For projects containing multiple performance obligations, the Company allocates the transaction price based on the estimated standalone selling price. The Company must develop assumptions that require judgment to determine the stand-alone selling price for each performance obligation identified in the contract. The Company utilizes key assumptions to determine the stand-alone selling price, which may include other comparable transactions, pricing considered in negotiating the transaction and the estimated costs. Variable consideration is allocated specifically to one or more performance obligations in a contract when the terms of the variable consideration relate to the satisfaction of the performance obligation and the resulting amounts allocated are consistent with the amounts the Company would expect to receive for the satisfaction of each performance obligation.

Cost of Sales

Selling, General and Administrative Expenses

Income Taxes

Leases

Stock-Based Compensation

Defined Contribution Plan

Basic and Diluted Earnings per Common Share

The table below sets forth the weighted-average shares used at December 31 in calculating earnings (loss) per share:

	2023		2022
Basic weighted-average shares		30,348,000		30,289,000
Conversion of unsecured loan notes		—		—
Unexercised options and unvested restricted stock units		—		—
Diluted weighted-average shares		30,348,000		30,289,000

Risk Concentrations

Our FUEL CHEM technology segment is dependent, in part, upon a supply of magnesium hydroxide. Any adverse changes in the availability of this chemical will likely have an adverse impact on ongoing operation of our FUEL CHEM programs. Our supplier of magnesium hydroxide, Martin Marietta Magnesia Specialties, LLC (MMMS) assures the continuance of a stable supply from MMMS of magnesium hydroxide products for our requirements in the U.S. and Canada. MMMS supplies us with magnesium hydroxide products manufactured pursuant to our specifications and we have agreed to purchase from MMMS, and MMMS has agreed to supply, 100% of our requirements for such magnesium hydroxide products for our customers who purchase such products for delivery in the U.S. and Canada. There can be no assurance that we will be able to obtain a stable source of magnesium hydroxide in markets outside the U.S.

Treasury Stock

Recently Issued Accounting Pronouncements

Note 2 - Revenue Recognition

12 Months Ended

Dec. 31, 2023

Revenue from Contract with Customer [Text Block]

2. REVENUE RECOGNITION

Disaggregated Revenue by Product Technology

The following table presents our revenues disaggregated by product technology:

	Twelve Months Ended December 31,
	2023		2022
Air Pollution Control
Technology solutions	$	9,497	$	7,935
Spare parts		2,239		911
Ancillary revenue		1,747		1,751
Total Air Pollution Control technology		13,483		10,597
FUEL CHEM
FUEL CHEM technology solutions		13,598		16,344
Total Revenues	$	27,081	$	26,941

Disaggregated Revenue by Geography

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

	Twelve Months Ended December 31,
	2023		2022
United States	$	21,062	$	20,311
Foreign Revenues
Americas		577		213
Europe		3,064		2,888
Asia		2,378		3,529
Total Foreign Revenues		6,019		6,630
Total Revenues	$	27,081	$	26,941

Timing of Revenue Recognition

The following table presents the timing of our revenue recognition:

	Twelve Months Ended December 31,
	2023		2022
Products transferred at a point in time	$	17,584	$	18,849
Products and services transferred over time		9,497		8,092
Total Revenues	$	27,081	$	26,941

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 Consolidated Balance Sheets. In our 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. For the FUEL CHEM technology segment, deliveries made in the current period but billed in subsequent periods are also considered contract assets. These assets are reported on the Consolidated Balance Sheet on a contract-by-contract basis at the end of each reporting period. At December 31, 2023, 2022, and 2021 contract assets for APC technology projects were approximately $2,285, $3,082, and $1,277, respectively, and are included in accounts receivable on the consolidated balance sheets. There were no contract assets for the FUEL CHEM technology segment as of December 31, 2023, 2022, and 2021.

However, the Company will periodically bill in advance of costs incurred before revenue is recognized, resulting in contract liabilities. These liabilities are reported on the consolidated balance sheet on a contract-by-contract basis at the end of each reporting period. Contract liabilities were $1,279, $372, and $390 at December 31, 2023, 2022, and 2021, respectively, and are included in other accrued liabilities on the consolidated balance sheets.

As of December 31, 2023 and 2022 we had no construction contracts in progress that were identified as a loss contract.

Remaining Performance Obligations

Practical Expedients and Exemptions

Accounts Receivable

The components of accounts receivable are as follows:

	As of
	December 31, 2023			December 31, 2022
Trade receivables	$	4,300		$	4,605
Unbilled receivables		2,285			3,082
Other short-term receivables		255			152
Allowance for credit losses		(111	)		(110	)
Total accounts receivable	$	6,729		$	7,729

Note 3 - Income Taxes

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Text Block]

3. INCOME TAXES

The components of loss before taxes for the years ended December 31 are as follows:

Origin of (loss) income before taxes	2023			2022
United States	$	(1,772	)	$	(1,262	)
Foreign		303			(126	)
Loss before income taxes	$	(1,469	)	$	(1,388	)

Significant components of income tax benefit (expense) for the years ended December 31 are as follows:

	2023			2022
Current:
Federal	$	—		$	—
State		(19	)		(6	)
Foreign		(55	)		(10	)
Total current		(74	)		(16	)
Deferred:
Federal		2			(19	)
State		3			(19	)
Total deferred		5			(38	)
Income tax expense	$	(69	)	$	(54	)

	2023			2022
Provision at the U.S. federal statutory rate		21.0	%		21.0	%
State taxes, net of federal benefit		4.7	%		3.1	%
Foreign tax rate differential		(0.6	)%		0.4	%
Valuation allowance		(4.9	)%		(48.8	)%
Chile outside basis differential		—	%		0.4	%
Italy IRES/IREP		(3.8	)%		—	%
Accrual to return		(5.8	)%		3.1	%
Research and development credit		5.4	%		5.9	%
State rate change		(1.4	)%		9.5	%
Share based compensation		(6.7	)%		3.3	%
Other Deferred true up		(6.6	)%		—	%
Global Intangible Low-Taxed Income (GILTI) inclusion		(4.4	)%		—	%
Other		(1.7	)%		(1.8	)%
Income tax (expense) benefit effective rate		(4.8	)%		(3.9	)%

The deferred tax assets and liabilities at December 31 are as follows:

	2023			2022
Deferred tax assets:
Stock compensation expense	$	250		$	272
Goodwill		—			182
Royalty accruals		10			10
Bad debt allowance		52			53
Net operating loss carryforwards		12,048			12,158
Credit carry-forwards		1,134			1,058
Inventory reserve		153			233
Depreciation		548			585
Research and Development Costs		1,053			528
Other		606			471
Total deferred tax assets		15,854			15,550
Deferred tax liabilities:
Goodwill		(238	)		—
Intangible assets		(89	)		(100	)
Total deferred tax liabilities		(327	)		(100	)
Net deferred tax asset before valuation allowance		15,527			15,450
Valuation allowances for deferred tax assets		(15,699	)		(15,627	)
Net deferred tax liability	$	(172	)	$	(177	)

The change in the valuation allowance for deferred tax assets for the years ended December 31 is as follows:

Year	Balance at January 1		Charged to costs and expenses		(Deductions)/Other		Balance at December 31
2022	$	14,950		677		—	$	15,627
2023	$	15,627		72		—	$	15,699

For the years ended December 31, 2023 and 2022, there were $42 and $0 exercises of stock options, respectively.

The table below sets forth a reconciliation of the beginning and ending amount of unrecognized tax benefit.

Year	Balance at January 1		Change in positions taken in a current period		Balance at December 31
2022	$	265		28	$	293
2023	$	293		33	$	326

Note 4 - Common Stock

12 Months Ended

Dec. 31, 2023

Equity [Text Block]

4. COMMON STOCK

Note 5 - Treasury Stock

12 Months Ended

Dec. 31, 2023

Treasury Stock [Text Block]

5. TREASURY STOCK

Note 6 - Nil Coupon Non-redeemable Convertible Unsecured Loan Notes	12 Months Ended
	Dec. 31, 2023
Notes to Financial Statements
Debt Disclosure [Text Block]	11. DEBT FINANCING On June 30, 2022, the Company entered into an Investment Collateral Security agreement to use for the sole purpose of issuing standby letters of credit that replaces the former Cash Collateral agreement with BMO Harris. The Investment Collateral Security agreement requires us to pledge our investments as collateral for 150% of the aggregate face amount of outstanding standby letters of credit. The Company pays 250 basis points on the face values of outstanding letters of credit. There are no financial covenants set forth in the Investment Collateral Security agreement. At December 31, 2023, the Company had outstanding standby letters of credit totaling approximately $904 under the Investment Collateral Security agreement. At December 31, 2023, the investments held as collateral totaled $1,356. Fuel Tech is committed to reimbursing the issuing bank for any payments made by the bank under these instruments.
NIL Coupon Non-redeemable Convertible Unsecured Loan Notes [Member]
Notes to Financial Statements
Debt Disclosure [Text Block]	6. NIL COUPON NON-REDEEMABLE CONVERTIBLE UNSECURED LOAN NOTES At December 31, 2023 and 2022, we had a principal amount of $76 of nil coupon non-redeemable convertible unsecured perpetual loan notes (Loan Notes) outstanding. The Loan Notes are convertible at any time into common stock at rates of $6.50 and $11.43 per share, depending on the note. As of December 31, 2023, the nil coupon loan notes were convertible into 6,715 shares of common stock. Based on our closing stock price of $1.05 at December 31, 2023, the aggregate fair value of the common stock that the holders would receive if all the loan notes were converted would be approximately $7, which is less than the principal amount of the loans outstanding as of that date. The Loan Notes bear no interest and have no maturity date. They are repayable in the event of our dissolution and the holders do not have the option to cash-settle the notes. Accordingly, they have been classified within stockholders’ equity in the accompanying balance sheets. The notes do not hold distribution or voting rights unless and until converted into common stock. For the years ended December 31, 2023 and 2022, there were no Loan Notes repurchased by the Company.

Note 7 - Warrants

12 Months Ended

Dec. 31, 2023

Warrants Disclosure [Text Block]

7. WARRANTS

The issuance of warrants to purchase shares of the Company's common stock are summarized as follows:

	Shares
Outstanding as of December 31, 2022		2,850,000
Granted		—
Exercised		—
Outstanding as of December 31, 2023		2,850,000

The following table summarizes information about warrants outstanding and exercisable at December 31, 2023:

		Number		Weighted-Average
		Outstanding/		Remaining Life		Weighted-Average
Range of Exercise Price		Exercisable		in Years		Exercise Price
$	5.10		2,500,000		2.62	$	5.10
$	6.45		350,000		2.62	$	6.45
			2,850,000

Note 8 - Stock-based Compensation

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Text Block]

8. STOCK-BASED COMPENSATION

	For the Year Ended December 31,
	2023		2022
Stock options and restricted stock units, net of forfeitures	$	389	$	224
After-tax effect of stock based compensation	$	389	$	224

Stock Options

There were no stock options granted during the years ended December 31, 2023 and 2022.

The following table presents a summary of our stock option activity and related information for the years ended December 31:

	2023					2022
	Number of Options			Weighted-Average Exercise Price		Number of Options			Weighted-Average Exercise Price
Outstanding at beginning of year		384,500		$	2.98		434,500		$	3.05
Granted		—			—		—			—
Exercised		(44,000	)		0.96		—			—
Expired or forfeited		(70,000	)		3.85		(50,000	)		3.55
Outstanding at end of year		270,500		$	3.09		384,500		$	2.98
Exercisable at end of year		270,500		$	3.09		384,500		$	2.98
Weighted-Average Remaining Contractual Life (years)					1.56					2.43
Aggregate Intrinsic Value				$	4				$	27

The following table summarizes information about stock options outstanding at December 31, 2023:

Options Outstanding and Exercisable
Range of Exercise Prices	Number of Options		Weighted-Average Remaining Contractual Life (years)		Weighted-Average Exercise Price
$0.96 - $1.27		44,000		3.9	$	0.97
$1.28 - $2.01		27,000		2.4		1.58
$2.02 - $3.83		105,000		1.4		2.44
$3.84 - $5.22		94,500		0.4		5.22
		270,500		1.6	$	3.09

Restricted Stock Units

A summary of restricted stock unit activity for the years ended December 31, 2023 and 2022 is as follows:

	*Shares*			*Weighted Average Grant Date Fair Value*
Unvested restricted stock units at December 31, 2021		45,003		$	1.51
Granted		807,048			1.32
Forfeited		(40,000	)		1.32
Vested		(45,003	)		1.51
Unvested restricted stock units at December 31, 2022		767,048			1.32
Granted		1,040,200			1.26
Forfeited		—			—
Vested		(45,000	)		1.37
Unvested restricted stock units at December 31, 2023		1,762,248		$	1.29

Deferred Directors Fees

Note 9 - Commitments and Contingencies

12 Months Ended

Dec. 31, 2023

Commitments and Contingencies Disclosure [Text Block]

9. COMMITMENTS AND CONTINGENCIES

Performance Guarantees

•

in support of the warranty period defined in the contract; or

•

in support of the system performance criteria that are defined in the contract.

Product Warranties

Note 10 - Leases

12 Months Ended

Dec. 31, 2023

Lessee, Operating Leases [Text Block]

10. LEASES

The terms of the Company’s three primary office space lease arrangements are as follows:

•

The Gallarate, Italy building lease, for approximately 1,335 square feet, runs through April 30, 2025. This facility serves as the operating headquarters for our European operations.

•

The Aurora, IL warehouse lease, for approximately 11,000 square feet, runs through March 31, 2031. This facility serves as an outside warehouse facility.

•

The Overland Park, KS lease, for approximately 600 square feet, runs through October 15, 2024. This facility serves primarily as a sales office.

Total operating lease expense is as follows:

		2023		2022
Operating lease cost	$	188	$	176
Short-term lease cost		15		29
Total lease cost	$	203	$	205

The weighted average remaining lease term was 6.58 years as of December 31, 2023. The weighted average discount rate was 8.00% as of December 31, 2023.

Remaining maturities of our existing lease liabilities as of December 31, 2023 were as follows:

Year Ending December 31,	Operating Leases
2024	$	133
2025		113
2026		103
2027		106
2028		110
Thereafter		258
Total lease payments	$	823
Less imputed interest		(209	)
Total	$	614

The following is the balance sheet classification of our existing lease liabilities:

	2023		2022
Operating lease liabilities - current	$	81	$	125
Operating lease liabilities - non-current		533		66
Total operating lease liabilities	$	614	$	191

Supplemental cash flow information related to leases was as follows:

	For the Twelve Months ended December 31, 2023		For the twelve months ended December 31, 2022
Cash paid for amounts included in the measurement of lease liabilities	$	150	$	157
Leased assets obtained in exchange for operating lease liabilities		533		139

Note 11 - Debt Financing

12 Months Ended

Dec. 31, 2023

Debt Disclosure [Text Block]

11. DEBT FINANCING

Note 12 - Business Segment and Geographic Financial Data

12 Months Ended

Dec. 31, 2023

Segment Reporting Disclosure [Text Block]

12. BUSINESS SEGMENT AND GEOGRAPHIC FINANCIAL DATA

Business Segment Financial Data

We segregate our financial results into two reportable segments representing two broad technology segments as follows:

•

The Air Pollution Control technology segment includes technologies to reduce NOx emissions in flue gas generated by the firing of natural gas or coal from boilers, incinerators, furnaces and other stationary combustion sources. These include NOxOUT^® and HERT™ Selective Non-Catalytic Reduction systems and Selective Catalytic Reduction (SCR) systems. Our SCR systems can also include Ammonia Injection Grid, and GSG™ Graduated Straightening Grid systems to provide high NOx reductions at significantly lower capital and operating costs than conventional SCR systems. ULTRA^® technology creates ammonia at a plant site using safe urea for use with any SCR application. ESP technologies make use of electrostatic precipitator products and services to reduce particulate matter. FGC systems are chemical injection systems offered in markets outside the U.S. and Canada to enhance electrostatic precipitator and fabric filter performance in controlling particulate emissions.

•

The “Other” classification includes those profit and loss items not allocated to either reportable segment. There are no inter-segment sales that require elimination.

Information about reporting segment net sales and gross margin from continuing operations are provided below:

For the year ended December 31, 2023	Air Pollution Control Segment			FUEL CHEM Segment			Other			Total
Revenues from external customers	$	13,483		$	13,598		$	—		$	27,081
Cost of sales		(8,410	)		(7,015	)		—			(15,425	)
Gross margin		5,073			6,583			—			11,656
Selling, general and administrative		—			—			(12,803	)		(12,803	)
Research and development		—			—			(1,511	)		(1,511	)
Operating income (loss) from continuing operations	$	5,073		$	6,583		$	(14,314	)	$	(2,658	)

For the year ended December 31, 2022	Air Pollution Control Segment			FUEL CHEM Segment			Other			Total
Revenues from external customers	$	10,597		$	16,344		$	—		$	26,941
Cost of sales		(6,924	)		(8,374	)		—			(15,298	)
Gross margin		3,673			7,970			—			11,643
Selling, general and administrative		—			—			(12,275	)		(12,275	)
Research and development		—			—			(895	)		(895	)
Operating income (loss) from continuing operations	$	3,673		$	7,970		$	(13,170	)	$	(1,527	)

Geographic Segment Financial Data

For the years ended December 31,	2023		2022
Revenues:
United States	$	21,062	$	20,311
Foreign		6,019		6,630
	$	27,081	$	26,941

As of December 31,	2023		2022
Assets:
United States	$	46,487	$	47,007
Foreign		3,901		3,117
	$	50,388	$	50,124

Note 13 - Restructuring Activities

12 Months Ended

Dec. 31, 2023

Restructuring and Related Activities Disclosure [Text Block]

13. RESTRUCTURING ACTIVITIES

The following table presents our revenues and net loss in China for the years ended December 31, 2023 and 2022:

	2023			2022
Total revenues	$	2		$	3
Net loss		(50	)		(209	)

The following table presents net assets in China as of December 31, 2023 and 2022:

	2023		2022
Total assets	$	846	$	929
Total liabilities		67		79
Total net assets	$	779	$	850

Total assets primarily consist of cash and other receivables. Total liabilities consist of accounts payable and certain accrued liabilities.

The Company recorded no restructuring charges for the years ended December 31, 2023 and 2022.

Note 14 - Accrued Liabilities

12 Months Ended

Dec. 31, 2023

Accounts Payable, Accrued Liabilities, and Other Liabilities Disclosure, Current [Text Block]

14. ACCRUED LIABILITIES

The components of other accrued liabilities are as follows:

	As of
	December 31, 2023		December 31, 2022
Contract liabilities (Note 2)	$	1,279	$	372
Warranty reserve (Note 9)		159		159
Deferred revenue		103		75
Accrued professional fees		101		—
Other accrued liabilities		292		220
Total other accrued liabilities	$	1,934	$	826

Insider Trading Arrangements	12 Months Ended
Insider Trading Arrangements	Dec. 31, 2023
Insider Trading Arr Line Items
Material Terms of Trading Arrangement [Text Block]	ITEM 9B - OTHER INFORMATION None
Rule 10b5-1 Arrangement Adopted [Flag]	false
Non-Rule 10b5-1 Arrangement Adopted [Flag]	false
Rule 10b5-1 Arrangement Terminated [Flag]	false
Non-Rule 10b5-1 Arrangement Terminated [Flag]	false

Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Basis of Accounting, Policy [Policy Text Block]

Basis of Presentation

The consolidated financial statements include the accounts of Fuel Tech and its wholly owned subsidiaries.

Geopolitical And Unexpected Events [Policy Text Block]

Geopolitical and Unexpected Events

Liquidity, Policy [Policy Text Block]

Liquidity

Use of Estimates, Policy [Policy Text Block]

Use of Estimates

Fair Value Measurement, Policy [Policy Text Block]

Fair Value Measurements

The carrying values of cash and cash equivalents, accounts receivable, and accounts payable are reasonable estimates of their fair value due to their short-term nature.

•

Level 1 – Observable inputs to the valuation methodology such as quoted prices in active markets for identical assets or liabilities

•

Cash and Cash Equivalents, Restricted Cash and Cash Equivalents, Policy [Policy Text Block]

Cash and cash equivalents

	December 31, 2023		December 31, 2022
Cash	$	12,495	$	12,560
Cash equivalents		5,083		10,768
Total cash and cash equivalents shown in the Consolidated Statements of Cash Flows	$	17,578	$	23,328

Investment, Policy [Policy Text Block]

Investments

The following table provides the amortized cost, gross unrealized gains and losses, and fair value of our HTM debt securities:

	December 31,
	2023			2022
Held-to-maturity debt securities:
Amortized cost	$	15,800		$	9,341
Gross unrecognized gains		—			—
Gross unrecognized losses		(86	)		(168	)
Fair value	$	15,714		$	9,173

The following table provides the amortized cost and fair value of debt securities by maturities at December 31, 2023:

	Amortized Cost		Fair Value
Within one year	$	12,136	$	12,056
After one year through two years		3,664		3,658
Total	$	15,800	$	15,714

Foreign Currency Risk Management [Policy Text Block]

Foreign Currency Risk Management

Accounts Receivable [Policy Text Block]

Accounts Receivable

Receivables, Trade and Other Accounts Receivable, Allowance for Doubtful Accounts, Policy [Policy Text Block]

Allowance for Credit Losses

Year	Balance at January 1		Provision charged to expense			Write-offs / Recoveries			Balance at December 31
2022	$	223	$	(19	)	$	(94	)	$	110
2023	$	110	$	24		$	(23	)	$	111

Prepaid Expenses and Other Current Assets [Policy Text Block]

Prepaid expenses and other current assets

Prepaid expenses and other current assets are short-term commitments of typically three to six months for future payments and can be redeemed at a discount or applied to future vendor payments.

Inventory, Policy [Policy Text Block]

Inventories

Inventories consist primarily of equipment constructed for resale and spare parts and are stated at the lower of cost or net realizable value, using the weighted-average cost method. At December 31, 2023 and 2022, inventory included equipment constructed for resale of$207 and $207, respectively, and spare parts, net of reserves of $232 and $185, respectively. Usage is recorded in cost of sales in the period that parts were issued to a project, used to service equipment, or sold to customers. Equipment constructed for resale that is in process is recorded in Other assets. In process equipment for inventory recorded as other assets was $618 and $634 as of December 31, 2023 and 2022, respectively.

Year	Balance at January 1		Provision charged to expense			Write-offs / Recoveries			Balance at December 31
2022	$	927	$	—		$	—		$	927
2023	$	927	$	(56	)	$	(258	)	$	613

Foreign Currency Transactions and Translations Policy [Policy Text Block]

Foreign Currency Translation and Transactions

Accumulated Other Comprehensive Income (Loss), Policy [Policy Text Block]

Accumulated Other Comprehensive Loss

	December 31,
	2023			2022
Foreign currency translation
Balance at beginning of period	$	(1,728	)	$	(1,604	)
Other comprehensive loss:
Foreign currency translation adjustments (1)		(20	)		(124	)
Balance at end of period	$	(1,748	)	$	(1,728	)
Total accumulated other comprehensive loss	$	(1,748	)	$	(1,728	)

(1)	In all periods presented, there were no tax impacts related to functional currency translation adjustments.

Research and Development Expense, Policy [Policy Text Block]

Research and Development

Standard Product Warranty, Policy [Policy Text Block]

Product/System Warranty

Goodwill and Intangible Assets, Policy [Policy Text Block]

Goodwill

Other Intangible Assets

During the years ended December 31, 2023 and 2022, Fuel Tech recorded no patent or trademark abandonment charges.

			2023							2022
Description of Other Intangibles	Amortization Period (years)		Gross Carrying Amount		Accumulated Amortization			Net Carrying Amount		Gross Carrying Amount		Accumulated Amortization			Net Carrying Amount
Patent assets		1 - 20		826		(468	)		358		803		(406	)		397
Total			$	826	$	(468	)	$	358	$	803	$	(406	)	$	397

The table below shows the estimated future amortization expense for intangible assets:

Year	Estimated Amortization Expense
2024	$	54
2025		33
2026		32
2027		32
2028		32
Thereafter		175
Total	$	358

Property, Plant and Equipment, Policy [Policy Text Block]

Property and Equipment

Description of Property and Equipment	Depreciable Life (years)		2023			2022
Land			$	1,050		$	1,050
Building		39		3,950			3,950
Building and leasehold improvements		3 - 39		2,655			2,626
Field equipment		3 - 4		12,100			11,882
Computer equipment and software		2 - 3		2,049			2,117
Furniture and fixtures		3 - 10		1,307			1,306
Vehicles		5		32			32
Construction in process				99			29
Total cost				23,242			22,992
Less accumulated depreciation				(18,703	)		(18,557	)
Total net book value			$	4,539		$	4,435

Revenue [Policy Text Block]

Revenue Recognition

The Company recognizes revenue when control of the promised goods or services is transferred to our customers, in an amount that reflects the consideration we expect to be entitled to in exchange for those goods or services. The majority of our contracts have a single performance obligation as the promise to transfer the individual goods or services is not separately identifiable from other promises in the contracts and, therefore, not distinct. Revenue is measured as the amount of consideration we expect to receive in exchange for transferring goods or providing services. Sales, value add, and other taxes we collect concurrent with revenue-producing activities are excluded from revenue.

Air Pollution Control Technology

FUEL CHEM

For projects containing multiple performance obligations, the Company allocates the transaction price based on the estimated standalone selling price. The Company must develop assumptions that require judgment to determine the stand-alone selling price for each performance obligation identified in the contract. The Company utilizes key assumptions to determine the stand-alone selling price, which may include other comparable transactions, pricing considered in negotiating the transaction and the estimated costs. Variable consideration is allocated specifically to one or more performance obligations in a contract when the terms of the variable consideration relate to the satisfaction of the performance obligation and the resulting amounts allocated are consistent with the amounts the Company would expect to receive for the satisfaction of each performance obligation.

Cost of Goods and Service [Policy Text Block]

Cost of Sales

Selling, General and Administrative Expenses, Policy [Policy Text Block]

Selling, General and Administrative Expenses

Income Tax, Policy [Policy Text Block]

Income Taxes

Lessee, Leases [Policy Text Block]

Leases

Share-Based Payment Arrangement [Policy Text Block]

Stock-Based Compensation

Pension and Other Postretirement Plans, Nonpension Benefits, Policy [Policy Text Block]

Defined Contribution Plan

Earnings Per Share, Policy [Policy Text Block]

Basic and Diluted Earnings per Common Share

The table below sets forth the weighted-average shares used at December 31 in calculating earnings (loss) per share:

	2023		2022
Basic weighted-average shares		30,348,000		30,289,000
Conversion of unsecured loan notes		—		—
Unexercised options and unvested restricted stock units		—		—
Diluted weighted-average shares		30,348,000		30,289,000

Concentration Risk, Credit Risk, Policy [Policy Text Block]

Risk Concentrations

Our FUEL CHEM technology segment is dependent, in part, upon a supply of magnesium hydroxide. Any adverse changes in the availability of this chemical will likely have an adverse impact on ongoing operation of our FUEL CHEM programs. Our supplier of magnesium hydroxide, Martin Marietta Magnesia Specialties, LLC (MMMS) assures the continuance of a stable supply from MMMS of magnesium hydroxide products for our requirements in the U.S. and Canada. MMMS supplies us with magnesium hydroxide products manufactured pursuant to our specifications and we have agreed to purchase from MMMS, and MMMS has agreed to supply, 100% of our requirements for such magnesium hydroxide products for our customers who purchase such products for delivery in the U.S. and Canada. There can be no assurance that we will be able to obtain a stable source of magnesium hydroxide in markets outside the U.S.

Stockholders' Equity, Policy [Policy Text Block]

Treasury Stock

New Accounting Pronouncements, Policy [Policy Text Block]

Recently Issued Accounting Pronouncements

Note 1 - Organization and Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2023

Schedule of Cash and Cash Equivalents [Table Text Block]

	December 31, 2023		December 31, 2022
Cash	$	12,495	$	12,560
Cash equivalents		5,083		10,768
Total cash and cash equivalents shown in the Consolidated Statements of Cash Flows	$	17,578	$	23,328

Debt Securities, Held-to-Maturity [Table Text Block]

	December 31,
	2023			2022
Held-to-maturity debt securities:
Amortized cost	$	15,800		$	9,341
Gross unrecognized gains		—			—
Gross unrecognized losses		(86	)		(168	)
Fair value	$	15,714		$	9,173

Investments Classified by Contractual Maturity Date [Table Text Block]

	Amortized Cost		Fair Value
Within one year	$	12,136	$	12,056
After one year through two years		3,664		3,658
Total	$	15,800	$	15,714

Financing Receivable, Allowance for Credit Loss [Table Text Block]

Year	Balance at January 1		Provision charged to expense			Write-offs / Recoveries			Balance at December 31
2022	$	223	$	(19	)	$	(94	)	$	110
2023	$	110	$	24		$	(23	)	$	111

Schedule of Excess and Obsolete Inventory Reserve [Table Text Block]

Year	Balance at January 1		Provision charged to expense			Write-offs / Recoveries			Balance at December 31
2022	$	927	$	—		$	—		$	927
2023	$	927	$	(56	)	$	(258	)	$	613

Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]

	December 31,
	2023			2022
Foreign currency translation
Balance at beginning of period	$	(1,728	)	$	(1,604	)
Other comprehensive loss:
Foreign currency translation adjustments (1)		(20	)		(124	)
Balance at end of period	$	(1,748	)	$	(1,728	)
Total accumulated other comprehensive loss	$	(1,748	)	$	(1,728	)

Schedule of Finite-Lived Intangible Assets [Table Text Block]

			2023							2022
Description of Other Intangibles	Amortization Period (years)		Gross Carrying Amount		Accumulated Amortization			Net Carrying Amount		Gross Carrying Amount		Accumulated Amortization			Net Carrying Amount
Patent assets		1 - 20		826		(468	)		358		803		(406	)		397
Total			$	826	$	(468	)	$	358	$	803	$	(406	)	$	397

Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block]

Year	Estimated Amortization Expense
2024	$	54
2025		33
2026		32
2027		32
2028		32
Thereafter		175
Total	$	358

Property, Plant and Equipment [Table Text Block]

Description of Property and Equipment	Depreciable Life (years)		2023			2022
Land			$	1,050		$	1,050
Building		39		3,950			3,950
Building and leasehold improvements		3 - 39		2,655			2,626
Field equipment		3 - 4		12,100			11,882
Computer equipment and software		2 - 3		2,049			2,117
Furniture and fixtures		3 - 10		1,307			1,306
Vehicles		5		32			32
Construction in process				99			29
Total cost				23,242			22,992
Less accumulated depreciation				(18,703	)		(18,557	)
Total net book value			$	4,539		$	4,435

Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]

	2023		2022
Basic weighted-average shares		30,348,000		30,289,000
Conversion of unsecured loan notes		—		—
Unexercised options and unvested restricted stock units		—		—
Diluted weighted-average shares		30,348,000		30,289,000

Note 2 - Revenue Recognition (Tables)

12 Months Ended

Dec. 31, 2023

Disaggregation of Revenue [Table Text Block]

	Twelve Months Ended December 31,
	2023		2022
Air Pollution Control
Technology solutions	$	9,497	$	7,935
Spare parts		2,239		911
Ancillary revenue		1,747		1,751
Total Air Pollution Control technology		13,483		10,597
FUEL CHEM
FUEL CHEM technology solutions		13,598		16,344
Total Revenues	$	27,081	$	26,941

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

	Twelve Months Ended December 31,
	2023		2022
United States	$	21,062	$	20,311
Foreign Revenues
Americas		577		213
Europe		3,064		2,888
Asia		2,378		3,529
Total Foreign Revenues		6,019		6,630
Total Revenues	$	27,081	$	26,941

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

	Twelve Months Ended December 31,
	2023		2022
Products transferred at a point in time	$	17,584	$	18,849
Products and services transferred over time		9,497		8,092
Total Revenues	$	27,081	$	26,941

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

	As of
	December 31, 2023			December 31, 2022
Trade receivables	$	4,300		$	4,605
Unbilled receivables		2,285			3,082
Other short-term receivables		255			152
Allowance for credit losses		(111	)		(110	)
Total accounts receivable	$	6,729		$	7,729

Note 3 - Income Taxes (Tables)

12 Months Ended

Dec. 31, 2023

Schedule of Income before Income Tax, Domestic and Foreign [Table Text Block]

Origin of (loss) income before taxes	2023			2022
United States	$	(1,772	)	$	(1,262	)
Foreign		303			(126	)
Loss before income taxes	$	(1,469	)	$	(1,388	)

Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]

	2023			2022
Current:
Federal	$	—		$	—
State		(19	)		(6	)
Foreign		(55	)		(10	)
Total current		(74	)		(16	)
Deferred:
Federal		2			(19	)
State		3			(19	)
Total deferred		5			(38	)
Income tax expense	$	(69	)	$	(54	)

Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]

	2023			2022
Provision at the U.S. federal statutory rate		21.0	%		21.0	%
State taxes, net of federal benefit		4.7	%		3.1	%
Foreign tax rate differential		(0.6	)%		0.4	%
Valuation allowance		(4.9	)%		(48.8	)%
Chile outside basis differential		—	%		0.4	%
Italy IRES/IREP		(3.8	)%		—	%
Accrual to return		(5.8	)%		3.1	%
Research and development credit		5.4	%		5.9	%
State rate change		(1.4	)%		9.5	%
Share based compensation		(6.7	)%		3.3	%
Other Deferred true up		(6.6	)%		—	%
Global Intangible Low-Taxed Income (GILTI) inclusion		(4.4	)%		—	%
Other		(1.7	)%		(1.8	)%
Income tax (expense) benefit effective rate		(4.8	)%		(3.9	)%

Schedule of Deferred Tax Assets and Liabilities [Table Text Block]

	2023			2022
Deferred tax assets:
Stock compensation expense	$	250		$	272
Goodwill		—			182
Royalty accruals		10			10
Bad debt allowance		52			53
Net operating loss carryforwards		12,048			12,158
Credit carry-forwards		1,134			1,058
Inventory reserve		153			233
Depreciation		548			585
Research and Development Costs		1,053			528
Other		606			471
Total deferred tax assets		15,854			15,550
Deferred tax liabilities:
Goodwill		(238	)		—
Intangible assets		(89	)		(100	)
Total deferred tax liabilities		(327	)		(100	)
Net deferred tax asset before valuation allowance		15,527			15,450
Valuation allowances for deferred tax assets		(15,699	)		(15,627	)
Net deferred tax liability	$	(172	)	$	(177	)

Summary of Valuation Allowance [Table Text Block]

Year	Balance at January 1		Charged to costs and expenses		(Deductions)/Other		Balance at December 31
2022	$	14,950		677		—	$	15,627
2023	$	15,627		72		—	$	15,699

Schedule of Unrecognized Tax Benefits Roll Forward [Table Text Block]

Year	Balance at January 1		Change in positions taken in a current period		Balance at December 31
2022	$	265		28	$	293
2023	$	293		33	$	326

Note 7 - Warrants (Tables)

12 Months Ended

Dec. 31, 2023

Schedule of Warrant Activity [Table Text Block]

	Shares
Outstanding as of December 31, 2022		2,850,000
Granted		—
Exercised		—
Outstanding as of December 31, 2023		2,850,000

Schedule of Stockholders' Equity Note, Warrants or Rights [Table Text Block]

		Number		Weighted-Average
		Outstanding/		Remaining Life		Weighted-Average
Range of Exercise Price		Exercisable		in Years		Exercise Price
$	5.10		2,500,000		2.62	$	5.10
$	6.45		350,000		2.62	$	6.45
			2,850,000

Note 8 - Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block]

	For the Year Ended December 31,
	2023		2022
Stock options and restricted stock units, net of forfeitures	$	389	$	224
After-tax effect of stock based compensation	$	389	$	224

Share-Based Payment Arrangement, Option, Activity [Table Text Block]

	2023					2022
	Number of Options			Weighted-Average Exercise Price		Number of Options			Weighted-Average Exercise Price
Outstanding at beginning of year		384,500		$	2.98		434,500		$	3.05
Granted		—			—		—			—
Exercised		(44,000	)		0.96		—			—
Expired or forfeited		(70,000	)		3.85		(50,000	)		3.55
Outstanding at end of year		270,500		$	3.09		384,500		$	2.98
Exercisable at end of year		270,500		$	3.09		384,500		$	2.98
Weighted-Average Remaining Contractual Life (years)					1.56					2.43
Aggregate Intrinsic Value				$	4				$	27

Share-Based Payment Arrangement, Option, Exercise Price Range [Table Text Block]

Options Outstanding and Exercisable
Range of Exercise Prices	Number of Options		Weighted-Average Remaining Contractual Life (years)		Weighted-Average Exercise Price
$0.96 - $1.27		44,000		3.9	$	0.97
$1.28 - $2.01		27,000		2.4		1.58
$2.02 - $3.83		105,000		1.4		2.44
$3.84 - $5.22		94,500		0.4		5.22
		270,500		1.6	$	3.09

Schedule of Nonvested Restricted Stock Units Activity [Table Text Block]

	*Shares*			*Weighted Average Grant Date Fair Value*
Unvested restricted stock units at December 31, 2021		45,003		$	1.51
Granted		807,048			1.32
Forfeited		(40,000	)		1.32
Vested		(45,003	)		1.51
Unvested restricted stock units at December 31, 2022		767,048			1.32
Granted		1,040,200			1.26
Forfeited		—			—
Vested		(45,000	)		1.37
Unvested restricted stock units at December 31, 2023		1,762,248		$	1.29

Note 10 - Leases (Tables)

12 Months Ended

Dec. 31, 2023

Lease, Cost [Table Text Block]

		2023		2022
Operating lease cost	$	188	$	176
Short-term lease cost		15		29
Total lease cost	$	203	$	205

Lessee, Operating Lease, Liability, to be Paid, Maturity [Table Text Block]

Year Ending December 31,	Operating Leases
2024	$	133
2025		113
2026		103
2027		106
2028		110
Thereafter		258
Total lease payments	$	823
Less imputed interest		(209	)
Total	$	614

Operating Lease Liabilities [Table Text Block]

	2023		2022
Operating lease liabilities - current	$	81	$	125
Operating lease liabilities - non-current		533		66
Total operating lease liabilities	$	614	$	191

Lessee, Operating Leases, Supplemental Cash Flow Information [Table Text Block]

	For the Twelve Months ended December 31, 2023		For the twelve months ended December 31, 2022
Cash paid for amounts included in the measurement of lease liabilities	$	150	$	157
Leased assets obtained in exchange for operating lease liabilities		533		139

Note 12 - Business Segment and Geographic Financial Data (Tables)

12 Months Ended

Dec. 31, 2023

Schedule of Segment Reporting Information, by Segment [Table Text Block]

For the year ended December 31, 2023	Air Pollution Control Segment			FUEL CHEM Segment			Other			Total
Revenues from external customers	$	13,483		$	13,598		$	—		$	27,081
Cost of sales		(8,410	)		(7,015	)		—			(15,425	)
Gross margin		5,073			6,583			—			11,656
Selling, general and administrative		—			—			(12,803	)		(12,803	)
Research and development		—			—			(1,511	)		(1,511	)
Operating income (loss) from continuing operations	$	5,073		$	6,583		$	(14,314	)	$	(2,658	)

For the year ended December 31, 2022	Air Pollution Control Segment			FUEL CHEM Segment			Other			Total
Revenues from external customers	$	10,597		$	16,344		$	—		$	26,941
Cost of sales		(6,924	)		(8,374	)		—			(15,298	)
Gross margin		3,673			7,970			—			11,643
Selling, general and administrative		—			—			(12,275	)		(12,275	)
Research and development		—			—			(895	)		(895	)
Operating income (loss) from continuing operations	$	3,673		$	7,970		$	(13,170	)	$	(1,527	)

Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas [Table Text Block]

For the years ended December 31,	2023		2022
Revenues:
United States	$	21,062	$	20,311
Foreign		6,019		6,630
	$	27,081	$	26,941

As of December 31,	2023		2022
Assets:
United States	$	46,487	$	47,007
Foreign		3,901		3,117
	$	50,388	$	50,124

Note 13 - Restructuring Activities (Tables)

12 Months Ended

Dec. 31, 2023

Restructuring and Related Costs [Table Text Block]

	2023			2022
Total revenues	$	2		$	3
Net loss		(50	)		(209	)

	2023		2022
Total assets	$	846	$	929
Total liabilities		67		79
Total net assets	$	779	$	850

Note 14 - Accrued Liabilities (Tables)

12 Months Ended

Dec. 31, 2023

Other Current Liabilities [Table Text Block]

	As of
	December 31, 2023		December 31, 2022
Contract liabilities (Note 2)	$	1,279	$	372
Warranty reserve (Note 9)		159		159
Deferred revenue		103		75
Accrued professional fees		101		—
Other accrued liabilities		292		220
Total other accrued liabilities	$	1,934	$	826

Note 1 - Organization and Significant Accounting Policies (Details Textual) $ in Thousands	12 Months Ended
	Dec. 31, 2023 USD ($) shares	Dec. 31, 2022 USD ($) shares	Jun. 30, 2022 USD ($)	Dec. 31, 2021 shares
Cash	$ 12,495	$ 12,560
Investment Plan, Maximum Amount. Approved			$ 10,000
Investment Plan, Maximum Additional Amount, Approved		10,000
Unbilled Contracts Receivable	2,285	3,082
Inventory, Net	$ 439	392
Number of Reporting Units	2
Goodwill	$ 2,116	2,116
Goodwill, Impairment Loss	0	0
Amortization of Intangible Assets	61	88
Depreciation	281	352
Defined Contribution Plan, Cost	$ 233	$ 200
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Number (in shares) \| shares	270,500	384,500		434,500
Class of Warrant or Right, Outstanding (in shares) \| shares	2,850,000	2,850,000
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount (in shares) \| shares	246,500	42,600
Treasury Stock, Shares, Acquired (in shares) \| shares	0	12,497
Treasury Stock, Value, Acquired, Cost Method	$ 0	$ 17
Revenue Benchmark [Member] \| Customer Concentration Risk [Member] \| Two Customers [Member]
Number of Major Customers	2
Concentration Risk, Percentage	36.00%
Revenue Benchmark [Member] \| Customer Concentration Risk [Member] \| Three Customers [Member]
Number of Major Customers		3
Concentration Risk, Percentage		48.00%
Antidilutive [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Number (in shares) \| shares	390,900	763,800
Class of Warrant or Right, Outstanding (in shares) \| shares	2,850,000
The 2014 Long-term Incentive Plan [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Authorized (in shares) \| shares	5,884,076
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Available for Grant (in shares) \| shares	645,650
Capitalized Third-party Costs [Member]
Finite-Lived Patents, Gross	$ 28	$ 37
FUEL CHEM Technology Segment [Member]
Goodwill	$ 2,116	$ 2,116
FUEL CHEM Technology Segment [Member] \| Revenue Benchmark [Member] \| Customer Concentration Risk [Member] \| Two Customers [Member]
Number of Major Customers	2
APC Technology [Member] \| Revenue Benchmark [Member] \| Customer Concentration Risk [Member] \| One Customer [Member]
Number of Major Customers		1
Equipment Contstructed for Resale [Member]
Inventory, Net	$ 207	$ 207
Spare Parts [Member]
Inventory, Net	232	185
In Process Equipment [Member]
Inventory, Net	$ 618	634
Minimum [Member]
Debt Securities, Held-to-maturity, Maturity Term (Month)	3 months
Standard Product Warranty Period (Year)	1 year
Minimum [Member] \| APC Technology [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period (Month)	6 months
Maximum [Member]
Debt Securities, Held-to-maturity, Maturity Term (Month)	36 months
Standard Product Warranty Period (Year)	2 years
Maximum [Member] \| APC Technology [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period (Month)	18 months
Asset Pledged as Collateral [Member] \| Letter of Credit [Member]
Restricted Cash and Investments	$ 1,356
Asset Pledged as Collateral [Member] \| Letter of Credit [Member] \| Varying Maturity Dates Expiring No Later Than September 30, 2024 [Member]
Restricted Cash and Investments	904
Non-US [Member]
Revenues	$ 6,019	$ 6,630
Percentage of Revenue	22.00%	25.00%
CHINA
Cash	$ 601
ITALY
Cash	821
CHILE
Cash	$ 200

Note 1 - Organization and Significant Accounting Policies - Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Cash	$ 12,495	$ 12,560
Cash equivalents	5,083	10,768
Total cash and cash equivalents shown in the Consolidated Statements of Cash Flows	$ 17,578	$ 23,328

Note 1 - Organization and Significant Accounting Policies - Amortized Cost to Fair Value of HTM Debt Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Amortized cost	$ 15,800	$ 9,341
Gross unrecognized gains	0	0
Gross unrecognized losses	(86)	(168)
Fair value	$ 15,714	$ 9,173

Note 1 - Organization and Significant Accounting Policies - Debt Securities by Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Within one year, amortized cost	$ 12,136
Within one year, fair value	12,056
After one year through two years, amortized cost	3,664
After one year through two years, fair value	3,658
Amortized cost	15,800	$ 9,341
Fair value	$ 15,714	$ 9,173

Note 1 - Organization and Significant Accounting Policies - Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Balance at January 1	$ 110	$ 223
Provision charged to expense	24	(19)
Write-offs / Recoveries	(23)	(94)
Balance at December 31	$ 111	$ 110

Note 1 - Organization and Significant Accounting Policies - Excess and Obsolete Inventory Reserve (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Excess and obsolete inventory reserve, beginning balance	$ 927	$ 927
Provision charged to expense	(56)	0
Write-offs / Recoveries	(258)	0
Excess and obsolete inventory reserve, ending balance	$ 613	$ 927

Note 1 - Organization and Significant Accounting Policies - Accumulated Other Comprehensive Income (Details) - USD ($)
$ in Thousands

12 Months Ended

Dec. 31, 2023

Dec. 31, 2022

$ 44,841

$ 46,200

Accumulated Foreign Currency Adjustment Attributable to Parent [Member]

43,714

44,841

Foreign currency translation adjustments (1)

(1,728)

(1,604)

^[1]

(20)

(124)