Fuel Tech (FTEK) 10-Q 9 May 23 2023 Q1 Quarterly report Financial data

Document And Entity Information

Document And Entity Information - shares	3 Months Ended
	Mar. 31, 2023	Apr. 28, 2023
Document Information [Line Items]
Entity Central Index Key	0000846913
Entity Registrant Name	FUEL TECH, INC.
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Period Focus	Q1
Document Fiscal Year Focus	2023
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2023
Document Transition Report	false
Entity File Number	001-33059
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	20-5657551
Entity Address, Address Line One	27601 Bella Vista Parkway
Entity Address, City or Town	Warrenville
Entity Address, State or Province	IL
Entity Address, Postal Zip Code	60555-1617
City Area Code	630
Local Phone Number	845-4500
Title of 12(b) Security	Common Stock
Trading Symbol	FTEK
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		30,296,297

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Current Period Unaudited) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 15,698	$ 23,328
Short-term investments	11,067	2,981
Accounts receivable, net	6,755	7,729
Inventories, net	509	392
Prepaid expenses and other current assets	1,350	1,395
Total current assets	35,379	35,825
Property and equipment, net of accumulated depreciation of $18,646 and $18,557, respectively	4,370	4,435
Goodwill	2,116	2,116
Other intangible assets, net of accumulated amortization of $418 and $406, respectively	401	397
Right-of-use operating lease assets, net	166	197
Long-term investments	7,054	6,360
Other assets	796	794
Total assets	50,282	50,124
Current liabilities:
Accounts payable	3,651	2,710
Accrued liabilities:
Operating lease liabilities - current	109	125
Employee compensation	588	1,105
Other accrued liabilities	827	826
Total current liabilities	5,175	4,766
Operating lease liabilities - non-current	51	66
Deferred income taxes, net	177	177
Other liabilities	277	274
Total liabilities	5,680	5,283
Stockholders’ equity:
Common stock, $.01 par value, 40,000,000 shares authorized, 31,272,303 and 31,272,303 shares issued, and 30,296,297 and 30,296,297 shares outstanding, respectively	313	313
Additional paid-in capital	164,511	164,422
Accumulated deficit	(116,405)	(115,991)
Accumulated other comprehensive loss	(1,642)	(1,728)
Nil coupon perpetual loan notes	76	76
Treasury stock, at cost	(2,251)	(2,251)
Total stockholders’ equity	44,602	44,841
Total liabilities and stockholders’ equity	$ 50,282	$ 50,124

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Current Period Unaudited) (Parentheticals) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Accumulated depreciation	$ 18,646	$ 18,557
Accumulated amortization, intangible assets	$ 418	$ 406
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	40,000,000	40,000,000
Common stock, shares issued (in shares)	31,272,303	31,272,303
Common stock, shares outstanding (in shares)	30,296,297	30,296,297

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Revenues	$ 7,287	$ 5,535
Costs and expenses:
Cost of sales	4,482	3,245
Selling, general and administrative	3,245	3,054
Research and development	218	220
Costs and Expenses	7,945	6,519
Operating loss	(658)	(984)
Interest expense	(5)	(5)
Interest income	339	1
Other expense, net	(90)	(10)
Loss before income taxes	(414)	(998)
Income tax expense	0	0
Net loss	$ (414)	$ (998)
Net loss per common share:
Basic net loss per common share (in dollars per share)	$ (0.01)	$ (0.03)
Diluted net loss per common share (in dollars per share)	$ (0.01)	$ (0.03)
Weighted-average number of common shares outstanding:
Basic (in shares)	30,296,000	30,267,000
Diluted (in shares)	30,296,000	30,267,000

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Income (Loss) (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Net loss	$ (414)	$ (998)
Other comprehensive income (loss):
Foreign currency translation adjustments	86	(70)
Comprehensive loss	$ (328)	$ (1,068)

Condensed Statements of Stockho

Condensed Statements of Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Common Stock Outstanding [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Nil Coupon Perpetual Loan Notes [Member]	Treasury Stock, Common [Member]	Total
Balance (in shares) at Dec. 31, 2021	30,264
Balance at Dec. 31, 2021	$ 312	$ 164,199	$ (114,549)	$ (1,604)	$ 76	$ (2,234)	$ 46,200
Net income (loss)	0	0	(998)	0	0	0	(998)
Foreign currency translation adjustments	0	0	0	(70)	0	0	(70)
Stock compensation expense	$ 0	18	0	0	0	0	18
Common shares issued upon vesting of restricted stock units (in shares)	45
Common shares issued upon vesting of restricted stock units	$ 1	(1)	0	0	0	0	0
Taxes paid on behalf of equity award participants (in shares)	(13)
Taxes paid on behalf of equity award participants	$ 0	0	0	0	0	(17)	(17)
Balance (in shares) at Mar. 31, 2022	30,296
Balance at Mar. 31, 2022	$ 313	164,216	(115,547)	(1,674)	76	(2,251)	45,133
Balance (in shares) at Dec. 31, 2022	30,296
Balance at Dec. 31, 2022	$ 313	164,422	(115,991)	(1,728)	76	(2,251)	44,841
Net income (loss)	0	0	(414)	0	0	0	(414)
Foreign currency translation adjustments	0	0	0	86	0	0	86
Stock compensation expense	$ 0	89	0	0	0	0	89
Balance (in shares) at Mar. 31, 2023	30,296
Balance at Mar. 31, 2023	$ 313	$ 164,511	$ (116,405)	$ (1,642)	$ 76	$ (2,251)	$ 44,602

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Operating Activities
Net loss	$ (414)	$ (998)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation	79	94
Amortization	11	14
Non-cash interest income on held-to-maturity securities	(95)	0
Provision for doubtful accounts, net of recoveries	0	(25)
Stock-based compensation, net of forfeitures	89	18
Changes in operating assets and liabilities:
Accounts receivable	990	(1,520)
Inventories	(116)	(13)
Prepaid expenses, other current assets and other non-current assets	51	(3)
Accounts payable	934	682
Accrued liabilities and other non-current liabilities	(519)	5
Net cash provided by (used in) operating activities	1,010	(1,746)
Investing Activities
Purchases of equipment and patents	(30)	(53)
Purchases of debt securities	(9,685)	0
Maturities of debt securities	1,000	0
Net cash used in investing activities	(8,715)	(53)
Financing Activities
Taxes paid on behalf of equity award participants	0	(17)
Net cash used in financing activities	0	(17)
Effect of exchange rate fluctuations on cash	75	2
Net decrease in cash, cash equivalents and restricted cash	(7,630)	(1,814)
Cash, cash equivalents, and restricted cash and cash equivalents at beginning of period (Note 2)	23,328	37,054
Cash, cash equivalents and restricted cash at end of period (Note 2)	$ 15,698	$ 35,240

Note 1 - General

Note 1 - General	3 Months Ended
	Mar. 31, 2023
Notes to Financial Statements
Organization, Consolidation and Presentation of Financial Statements Disclosure and Significant Accounting Policies [Text Block]	1. Organization Fuel Tech, Inc. and subsidiaries ("Fuel Tech", the "Company", "we", "us" or "our") develops and provides proprietary technologies for air pollution control, process optimization, water treatment, and advanced engineering services. These technologies enable customers to operate in a cost-effective and environmentally sustainable manner. The Company’s nitrogen oxide (NOx) reduction technologies reduce nitrogen oxide emissions from boilers, furnaces, and other stationary combustion sources. To reduce NOx emissions, our technologies utilize advanced combustion modification techniques and post-combustion NOx control approaches including non-catalytic, catalytic, and combined systems. The Company also provides solutions for the mitigation of particulate matter, including particulate control with electrostatic precipitator products and services, and using flue gas conditioning systems which modify the ash properties of particulate for improved collection efficiency. The Company’s FUEL CHEM® technology improves the efficiency, reliability, fuel flexibility, boiler heat rate, and environmental status of combustion units by controlling slagging, fouling, corrosion, and opacity. Water treatment technologies include DGI™ Dissolved Gas Infusion Systems which utilize a patented saturator vessel and a patent-pending channel injector to deliver supersaturated oxygen-water solutions and potentially other gas-liquid combinations to target process applications or environmental issues within the municipal and industrial water sectors. The infusion process has a variety of applications in the water and wastewater sector, including aquaculture, agriculture/horticulture, pulp & paper, tanneries, landfill leachate, irrigation, treatment of natural waters, wastewater odor management as well as supplying oxygen or other gases for biochemical reactions and pH adjustment. Many of Fuel Tech’s products and services rely heavily on the Company’s computational fluid dynamics modeling capabilities, which are enhanced by internally developed, high-end visualization software. Basis of Presentation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (U.S. GAAP) for interim financial information and with the instructions to Form 10 10 X not three March 31, 2023 not December 31, 2023. 10 December 31, 2022 COVID- 19 The effects of the coronavirus (COVID- 19 may third Geopolitical events and global economic sanctions resulting from the ongoing conflict between Russia and Ukraine may may Management cannot predict the full impact of the COVID- 19

Note 2 - Summary of Significant

Note 2 - Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2023
Notes to Financial Statements
Significant Accounting Policies [Text Block]	2. Restricted cash and cash equivalents Restricted cash as of March 31, 2022 June 2022, 10 The following table provides a reconciliation of cash, cash equivalents, and restricted cash and cash equivalents reported within the Condensed Consolidated Balance Sheets that sum to the total of the same such amounts shown in the Condensed Consolidated Statements of Cash Flows: March 31, March 31, 2023 2022 Cash $ 13,505 $ 34,174 Cash equivalents 2,193 — Restricted cash and cash equivalents included in current assets — 1,066 Total cash, cash equivalents, and restricted cash and cash equivalents shown in the Condensed Consolidated Statements of Cash Flows $ 15,698 $ 35,240 Investments In 2022, 10 March 31, 2023 , the amount of funds collateralized under the Investment Collateral Security agreement is $ relating to existing standby letters of credit that is comprised of $1,352 with varying maturity dates and expire no March 31, 2024 no November 30, 2025. We consider all highly liquid debt investments with original maturities from the date of purchase of three three Our investments in debt securities consist of United States (US) Treasury securities, including Notes, Bonds, and Bills, and US Government Agency securities, which are designated as held-to-maturity (HTM) and stated at amortized cost. The Company has the positive intent and ability to hold these investments to maturity and does not three thirty-six three three one one Our investments in debt securities consist of United States (US) Treasury securities, including Notes, Bonds, and Bills, and US Government Agency securities. Due to the creditworthiness of the entities issuing these securities, there is no The following table provides the amortized cost, gross unrealized gains and losses, and fair value of our HTM debt securities: As of Held-to-maturity debt securities: March 31, 2023 December 31, 2022 Amortized cost $ 18,121 $ 9,341 Gross unrecognized gains — — Gross unrecognized losses (148 ) (168 ) Fair value $ 17,973 $ 9,173 The following table provides the amortized cost and fair value of debt securities by maturities at March 31, 2023 Amortized Cost Fair Value Within one year $ 11,067 $ 11,012 After one year through two years 5,607 5,535 After two years through three years 1,447 1,426 Total $ 18,121 $ 17,973 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 March 31, 2023 and December 31, 2022 , inventory included equipment constructed for resale of $ and $ , respectively, and spare parts, net of reserves of $ and $ , 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 $634 and $634 as of March 31, 2023 and December 31, 2022 , respectively. In not Allowance for Credit Losses In June 2016, 2016 13, 326 November 2019, 2019 10, 326 815 842 January 1, 2023 not not January 1, 2023, For the general risk categories, the company uses historical losses over a fixed period, excluding certain write-off activity that were not zero The following table provides the roll forward of the allowance for credit loss: At January 1, 2022 $ 223 Provision charged to expense (19 ) (Write-offs) / Recoveries (94 ) At December 31, 2022 $ 110 Provision charged to expense — (Write-offs) / Recoveries — At March 31, 2023 $ 110

Note 3 - Revenue

Note 3 - Revenue	3 Months Ended
	Mar. 31, 2023
Notes to Financial Statements
Revenue from Contract with Customer [Text Block]	3. Disaggregated Revenue by Product Technology The following table presents our revenues disaggregated by product technology: Three Months Ended March 31, 2023 2022 Air Pollution Control Technology solutions $ 2,982 $ 1,841 Spare parts 174 96 Ancillary revenue 403 267 Total Air Pollution Control technology revenues 3,559 2,204 FUEL CHEM FUEL CHEM technology solutions 3,728 3,331 Total Revenues $ 7,287 $ 5,535 Disaggregated Revenue by Geography The following table presents our revenues disaggregated by geography, based on t he location of the end-user: Three Months Ended March 31, 2023 2022 United States $ 5,981 $ 3,688 Foreign Revenues Latin America — 69 Europe 579 404 Asia 727 1,374 Total Foreign Revenues 1,306 1,847 Total Revenues $ 7,287 $ 5,535 Timing of Revenue Recognition The following table presents the timing of our revenue recognition: Three Months Ended March 31, 2023 2022 Products transferred at a point in time $ 4,305 $ 3,694 Products and services transferred over time 2,982 1,841 Total Revenues $ 7,287 $ 5,535 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. For the FUEL CHEM technology segment, deliveries made in the current period but billed in subsequent periods are also considered unbilled receivables (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, 2023 December 31, 2022 December 31, 2021, March 31, 2023 December 31, 2022 December 31, 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 Condensed Consolidated Balance Sheets on a contract-by-contract basis at the end of each reporting period. Contract liabilities were $427, $372, and $390 at March 31, 2023 December 31, 2022 December 31, 2021, Changes in the contract asset and liability balances during the three March 31, 2023 not three March 31, 2023 three March 31, 2022 As of March 31, 2023 December 31, 2022 Remaining Performance Obligations Remaining performance obligations represents the transaction price of APC technology booked orders for which work has not As of March 31, 2023 , the aggregate amount of the transaction price allocated to remaining performance obligations was $ . The Company expects to recognize revenue on approximately $ 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, 2023 December 31, 2022 Trade receivables $ 3,295 $ 4,605 Unbilled receivables 3,444 3,082 Other short-term receivables 126 152 Allowance for credit losses (110 ) (110 ) Total accounts receivable $ 6,755 $ 7,729

Note 4 - Restructuring Activiti

Note 4 - Restructuring Activities	3 Months Ended
	Mar. 31, 2023
Notes to Financial Statements
Restructuring and Related Activities Disclosure [Text Block]	4. On January 18, 2019, March 31, 2023 The following table presents our revenues and net loss for 2023 2022 Three Months Ended March 31, 2023 2022 Total revenues $ — $ 1 Net loss (20 ) (13 ) Total assets primarily consist of cash and other receivables. Total liabilities consist of accounts payable and certain accrued liabilities. The following table presents net assets in China as follows: As of March 31, 2023 December 31, 2022 Total assets $ 913 $ 929 Total liabilities 80 79 Total net assets $ 833 $ 850

Note 5 - Accumulated Other Comp

Note 5 - Accumulated Other Comprehensive Loss	3 Months Ended
	Mar. 31, 2023
Notes to Financial Statements
Comprehensive Income (Loss) Note [Text Block]	5. The changes in accumulated other comprehensive loss by component were as follows: Three Months Ended March 31, 2023 2022 Foreign currency translation Balance at beginning of period $ (1,728 ) $ (1,604 ) Other comprehensive loss: Foreign currency translation adjustments (1) 86 (70 ) Total accumulated other comprehensive loss $ (1,642 ) $ (1,674 ) ( 1 In all periods presented, there were no no

Note 6 - Treasury Stock

Note 6 - Treasury Stock	3 Months Ended
	Mar. 31, 2023
Notes to Financial Statements
Treasury Stock [Text Block]	6. Common stock held in treasury totaled 976,006 with a cost of $2,251 at March 31, 2023 December 31, 2022

Note 7 - Earnings Per Share

Note 7 - Earnings Per Share	3 Months Ended
	Mar. 31, 2023
Notes to Financial Statements
Earnings Per Share [Text Block]	7. Basic earnings per share excludes the dilutive effects of stock options, restricted stock units (RSUs), warrants, and the nil nil ed. For the three -month periods ended March 31, 2023 2022 , basic earnings per share is equal to diluted earnings per share because all outstanding stock awards, warrants, and convertible loan notes are considered anti-dilutive during periods of net loss. The following table sets forth the weighted-average shares used in calculating the earnings per share for the three March 31, 2023 2022 Three Months Ended March 31, 2023 2022 Basic weighted-average shares 30,296,000 30,267,000 Conversion of unsecured loan notes — — Unexercised options and unvested RSUs — — Diluted weighted-average shares 30,296,000 30,267,000 For the three March 31, 2023 and 2022, and , respectively, and warrants of in both periods, which were antidilutive for the purpose of the calculation of diluted earnings per share. For the three March 31, 2023 2022, 26 6,000 and 56,000, respectively, incremental equity awards that were excluded from the computation of diluted earnings per share as the inclusion of such would have been anti-dilutive due to a net loss in the period. These equity awards could potentially dilute basic earnings per share in future years.

Note 8 - Stock-based Compensati

Note 8 - Stock-based Compensation	3 Months Ended
	Mar. 31, 2023
Notes to Financial Statements
Share-Based Payment Arrangement [Text Block]	8. Under our stock-based employee compensation plan, referred to as the Fuel Tech, Inc. 2014 may may may March 31, 2023 We did not three March 31, 2023 2022. no three March 31, 2023 2022. no Stock-based compensation is included in selling, general, and administrative costs in our Condensed Consolidated Statements of Operations. The components of stock-based compensation for the three March 31, 2023 2022 Three Months Ended March 31, 2023 2022 Stock options and restricted stock units, net of forfeitures $ 89 $ 18 After-tax effect of stock-based compensation $ 89 $ 18 Stock Options Stock options granted to employees under the Incentive Plans have a 10-year life and they vest as follows: 50% after the second third fourth four Fuel Tech uses the Black-Scholes option pricing model to estimate the grant date fair value of employee stock options. The principal variable assumptions utilized in valuing options and the methodology for estimating such model inputs include: ( 1 2 3 Stock option activity for Fuel Tech’s Incentive Plans for the three March 31, 2023 Weighted- Average Number Weighted- Remaining Aggregate of Average Contractual Intrinsic Options Exercise Price Term Value Outstanding on January 1, 2023 384,500 $ 2.98 Granted — — Exercised — — Expired or forfeited — — Outstanding on March 31, 2023 384,500 $ 2.98 2.19 $ 28 Exercisable on March 31, 2023 384,500 $ 2.98 2.19 $ 28 As of March 31, 2023 Restricted Stock Units RSUs granted to employees vest over time based on continued service (typically vesting over a period between two four ars), and RSUs granted to directors vest after a one d. At March 31, 2023 of unrecognized compensation cost related to all non-vested share-based compensation arrangements granted under the Incentive Plan. That cost is expected to be recognized over the remaining requisite service period of yea A summary of restricted stock unit activity for the three March 31, 2023 Weighted Average Grant Date Shares Fair Value Unvested restricted stock units at January 1, 2023 767,048 $ 1.32 Granted 100,000 1.25 Unvested restricted stock units at March 31, 2023 867,048 $ 1.31 Deferred Directors Fees In addition to the Incentive Plans, Fuel Tech has a Deferred Compensation Plan for Directors (Deferred Plan). Under the terms of the Deferred Plan, Directors can elect to defer Directors’ fees for shares of Fuel Tech Common Stock that are issuable at a future date as defined in the agreement. In accordance with Accounting Standards Codification (ASC) 718, three March 31, 2023 2022

Note 9 - Warrants

Note 9 - Warrants	3 Months Ended
	Mar. 31, 2023
Notes to Financial Statements
Warrants Disclosure [Text Block]	9. The following table summarizes information about warrants outstanding and exercisable at March 31, 2023 Range of Exercise Price Number Outstanding/Exercisable Weighted Average Remaining Life in Years Weighted Average Exercise Price $5.10 2,500,000 3.37 $ 5.10 $6.45 350,000 3.37 $ 6.45 2,850,000

Note 10 - Debt Financing

Note 10 - Debt Financing	3 Months Ended
	Mar. 31, 2023
Notes to Financial Statements
Debt Disclosure [Text Block]	10. On June 30, 2022, no March 31, 2023 , the Company had outstanding standby letters of credit totaling approximately $ under the Investment Collateral Security agreement. At March 31, 2023 , the investments held as collateral totaled $ . Fuel Tech is committed to reimbursing the issuing bank for any payments made by the bank under these instruments.

Note 11 - Business Segment and

Note 11 - Business Segment and Geographic Financial Data	3 Months Ended
	Mar. 31, 2023
Notes to Financial Statements
Segment Reporting Disclosure [Text Block]	11. Business Segment Financial Data We segregate our financial results into two reportable segments representing two • T he 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 Over-Fire Air systems, NOxOUT ® and HERT™ Selective Non-Catalytic Reduction systems, and Selective Catalytic Reduction (SCR) systems. Our SCR systems can also include Ammonia Injection Grid, and Graduated Straightening Grid GSG™ 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. Electrostatic Precipitator technologies make use of electrostatic precipitator products and services to reduce particulate matter. Flue Gas Conditioning 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 FUEL CHEM ® ® The “Other” classification includes those profit and loss items not no We evaluate performance and allocate resources based on reviewing gross margin by reportable segment. The accounting policies of the reportable segments are the same as those described in the summary of significant accounting policies (Note 1 10 not Information about reporting segment net sales and gross margin from operations are provided below: Air Pollution FUEL CHEM Three months ended March 31, 2023 Control Segment Segment Other Total Revenues from external customers $ 3,559 $ 3,728 $ — $ 7,287 Cost of sales (2,594 ) (1,888 ) — (4,482 ) Gross margin 965 1,840 — 2,805 Selling, general and administrative — — (3,245 ) (3,245 ) Research and development — — (218 ) (218 ) Operating income (loss) from operations $ 965 $ 1,840 $ (3,463 ) $ (658 ) Air Pollution FUEL CHEM Three months ended March 31, 2022 Control Segment Segment Other Total Revenues from external customers $ 2,204 $ 3,331 $ — $ 5,535 Cost of sales (1,429 ) (1,816 ) — (3,245 ) Gross margin 775 1,515 — 2,290 Selling, general and administrative — — (3,054 ) (3,054 ) Research and development — — (220 ) (220 ) Operating income (loss) from operations $ 775 $ 1,515 $ (3,274 ) $ (984 ) Geographic Segment Financial Data Information concerning our operations by geographic area is provided below. Revenues are attributed to countries based on the location of the end-user. Assets are those directly associated with operations of the geographic area. Three Months Ended March 31, 2023 2022 Revenues: United States $ 5,981 $ 3,688 Foreign 1,306 1,847 $ 7,287 $ 5,535 March 31, December 31, 2023 2022 Assets: United States $ 46,893 $ 47,007 Foreign 3,389 3,117 $ 50,282 $ 50,124

Note 12 - Accrued Liabilities

Note 12 - Accrued Liabilities	3 Months Ended
	Mar. 31, 2023
Notes to Financial Statements
Accounts Payable, Accrued Liabilities, and Other Liabilities Disclosure, Current [Text Block]	12. The components of other accrued liabilities are as follows: As of March 31, 2023 December 31, 2022 Contract liabilities (Note 3) $ 427 $ 372 Warranty reserve (Note 13) 159 159 Other accrued liabilities 241 295 Total other accrued liabilities $ 827 $ 826

Note 13 - Commitments and Conti

Note 13 - Commitments and Contingencies	3 Months Ended
	Mar. 31, 2023
Notes to Financial Statements
Commitments and Contingencies Disclosure [Text Block]	13. Fuel Tech is subject to various claims and contingencies related to, among other things, workers compensation, general liability (including product liability), and lawsuits. The Company records liabilities where a contingent loss is probable and can be reasonably estimated. If the reasonable estimate of a probable loss is a range, the Company records the most probable estimate of the loss or the minimum amount when no not not may From time to time we are involved in litigation with respect to matters arising from the ordinary conduct of our business. In the opinion of management, based upon presently available information, either adequate provision for anticipated costs have been accrued or the ultimate anticipated costs will not not Fuel Tech issues a standard product warranty with the sale of its products to customers. Our recognition of warranty liability is based primarily on analyses of warranty claims experienced in the preceding years as the nature of our historical product sales for which we offer a warranty are substantially unchanged. This approach provides an aggregate warranty accrual that is historically aligned with actual warranty claims experienced. There was no change in the warranty liability balance included in the other accrued liabilities line of the Condensed Consolidated Balance Sheets during the three March 31, 2023 2022 March 31, 2023 December 31, 2022

Note 14 - Income Taxes

Note 14 - Income Taxes	3 Months Ended
	Mar. 31, 2023
Notes to Financial Statements
Income Tax Disclosure [Text Block]	14. The Company’s effective tax rate is approximately 0.0% and for the three -month periods ended March 31, 2023 2022 three March 31, 2023 2022 no three March 31, 2023 2022 Fuel Tech had no unrecognized tax benefits as of March 31, 2023 December 31, 2022

Significant Accounting Policies

Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2023
Accounting Policies [Abstract]
Cash and Cash Equivalents, Restricted Cash and Cash Equivalents, Policy [Policy Text Block]	Restricted cash and cash equivalents Restricted cash as of March 31, 2022 June 2022, 10 The following table provides a reconciliation of cash, cash equivalents, and restricted cash and cash equivalents reported within the Condensed Consolidated Balance Sheets that sum to the total of the same such amounts shown in the Condensed Consolidated Statements of Cash Flows: March 31, March 31, 2023 2022 Cash $ 13,505 $ 34,174 Cash equivalents 2,193 — Restricted cash and cash equivalents included in current assets — 1,066 Total cash, cash equivalents, and restricted cash and cash equivalents shown in the Condensed Consolidated Statements of Cash Flows $ 15,698 $ 35,240
Investment, Policy [Policy Text Block]	Investments In 2022, 10 March 31, 2023 , the amount of funds collateralized under the Investment Collateral Security agreement is $ relating to existing standby letters of credit that is comprised of $1,352 with varying maturity dates and expire no March 31, 2024 no November 30, 2025. We consider all highly liquid debt investments with original maturities from the date of purchase of three three Our investments in debt securities consist of United States (US) Treasury securities, including Notes, Bonds, and Bills, and US Government Agency securities, which are designated as held-to-maturity (HTM) and stated at amortized cost. The Company has the positive intent and ability to hold these investments to maturity and does not three thirty-six three three one one Our investments in debt securities consist of United States (US) Treasury securities, including Notes, Bonds, and Bills, and US Government Agency securities. Due to the creditworthiness of the entities issuing these securities, there is no The following table provides the amortized cost, gross unrealized gains and losses, and fair value of our HTM debt securities: As of Held-to-maturity debt securities: March 31, 2023 December 31, 2022 Amortized cost $ 18,121 $ 9,341 Gross unrecognized gains — — Gross unrecognized losses (148 ) (168 ) Fair value $ 17,973 $ 9,173 The following table provides the amortized cost and fair value of debt securities by maturities at March 31, 2023 Amortized Cost Fair Value Within one year $ 11,067 $ 11,012 After one year through two years 5,607 5,535 After two years through three years 1,447 1,426 Total $ 18,121 $ 17,973
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 March 31, 2023 and December 31, 2022 , inventory included equipment constructed for resale of $ and $ , respectively, and spare parts, net of reserves of $ and $ , 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 $634 and $634 as of March 31, 2023 and December 31, 2022 , respectively. In not
Receivables, Trade and Other Accounts Receivable, Allowance for Doubtful Accounts, Policy [Policy Text Block]	Allowance for Credit Losses In June 2016, 2016 13, 326 November 2019, 2019 10, 326 815 842 January 1, 2023 not not January 1, 2023, For the general risk categories, the company uses historical losses over a fixed period, excluding certain write-off activity that were not zero The following table provides the roll forward of the allowance for credit loss: At January 1, 2022 $ 223 Provision charged to expense (19 ) (Write-offs) / Recoveries (94 ) At December 31, 2022 $ 110 Provision charged to expense — (Write-offs) / Recoveries — At March 31, 2023 $ 110

Note 2 - Summary of Significa_2

Note 2 - Summary of Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 2023
Notes Tables
Schedule of Cash and Cash Equivalents [Table Text Block]	March 31, March 31, 2023 2022 Cash $ 13,505 $ 34,174 Cash equivalents 2,193 — Restricted cash and cash equivalents included in current assets — 1,066 Total cash, cash equivalents, and restricted cash and cash equivalents shown in the Condensed Consolidated Statements of Cash Flows $ 15,698 $ 35,240
Debt Securities, Held-to-Maturity [Table Text Block]	As of Held-to-maturity debt securities: March 31, 2023 December 31, 2022 Amortized cost $ 18,121 $ 9,341 Gross unrecognized gains — — Gross unrecognized losses (148 ) (168 ) Fair value $ 17,973 $ 9,173
Investments Classified by Contractual Maturity Date [Table Text Block]	Amortized Cost Fair Value Within one year $ 11,067 $ 11,012 After one year through two years 5,607 5,535 After two years through three years 1,447 1,426 Total $ 18,121 $ 17,973
Financing Receivable, Allowance for Credit Loss [Table Text Block]	At January 1, 2022 $ 223 Provision charged to expense (19 ) (Write-offs) / Recoveries (94 ) At December 31, 2022 $ 110 Provision charged to expense — (Write-offs) / Recoveries — At March 31, 2023 $ 110

Note 3 - Revenue (Tables)

Note 3 - Revenue (Tables)	3 Months Ended
	Mar. 31, 2023
Notes Tables
Disaggregation of Revenue [Table Text Block]	Three Months Ended March 31, 2023 2022 Air Pollution Control Technology solutions $ 2,982 $ 1,841 Spare parts 174 96 Ancillary revenue 403 267 Total Air Pollution Control technology revenues 3,559 2,204 FUEL CHEM FUEL CHEM technology solutions 3,728 3,331 Total Revenues $ 7,287 $ 5,535
Revenue from External Customers by Geographic Areas [Table Text Block]	Three Months Ended March 31, 2023 2022 United States $ 5,981 $ 3,688 Foreign Revenues Latin America — 69 Europe 579 404 Asia 727 1,374 Total Foreign Revenues 1,306 1,847 Total Revenues $ 7,287 $ 5,535
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table Text Block]	Three Months Ended March 31, 2023 2022 Products transferred at a point in time $ 4,305 $ 3,694 Products and services transferred over time 2,982 1,841 Total Revenues $ 7,287 $ 5,535
Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block]	As of March 31, 2023 December 31, 2022 Trade receivables $ 3,295 $ 4,605 Unbilled receivables 3,444 3,082 Other short-term receivables 126 152 Allowance for credit losses (110 ) (110 ) Total accounts receivable $ 6,755 $ 7,729

Note 4 - Restructuring Activi_2

Note 4 - Restructuring Activities (Tables)	3 Months Ended
	Mar. 31, 2023
Notes Tables
Restructuring and Related Costs [Table Text Block]	Three Months Ended March 31, 2023 2022 Total revenues $ — $ 1 Net loss (20 ) (13 ) As of March 31, 2023 December 31, 2022 Total assets $ 913 $ 929 Total liabilities 80 79 Total net assets $ 833 $ 850

Note 5 - Accumulated Other Co_2

Note 5 - Accumulated Other Comprehensive Loss (Tables)	3 Months Ended
	Mar. 31, 2023
Notes Tables
Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]	Three Months Ended March 31, 2023 2022 Foreign currency translation Balance at beginning of period $ (1,728 ) $ (1,604 ) Other comprehensive loss: Foreign currency translation adjustments (1) 86 (70 ) Total accumulated other comprehensive loss $ (1,642 ) $ (1,674 )

Note 7 - Earnings Per Share (Ta

Note 7 - Earnings Per Share (Tables)	3 Months Ended
	Mar. 31, 2023
Notes Tables
Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]	Three Months Ended March 31, 2023 2022 Basic weighted-average shares 30,296,000 30,267,000 Conversion of unsecured loan notes — — Unexercised options and unvested RSUs — — Diluted weighted-average shares 30,296,000 30,267,000

Note 8 - Stock-based Compensa_2

Note 8 - Stock-based Compensation (Tables)	3 Months Ended
	Mar. 31, 2023
Notes Tables
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block]	Three Months Ended March 31, 2023 2022 Stock options and restricted stock units, net of forfeitures $ 89 $ 18 After-tax effect of stock-based compensation $ 89 $ 18
Share-Based Payment Arrangement, Option, Activity [Table Text Block]	Weighted- Average Number Weighted- Remaining Aggregate of Average Contractual Intrinsic Options Exercise Price Term Value Outstanding on January 1, 2023 384,500 $ 2.98 Granted — — Exercised — — Expired or forfeited — — Outstanding on March 31, 2023 384,500 $ 2.98 2.19 $ 28 Exercisable on March 31, 2023 384,500 $ 2.98 2.19 $ 28
Schedule of Nonvested Restricted Stock Units Activity [Table Text Block]	Weighted Average Grant Date Shares Fair Value Unvested restricted stock units at January 1, 2023 767,048 $ 1.32 Granted 100,000 1.25 Unvested restricted stock units at March 31, 2023 867,048 $ 1.31

Note 9 - Warrants (Tables)

Note 9 - Warrants (Tables)	3 Months Ended
	Mar. 31, 2023
Notes Tables
Schedule of Stockholders' Equity Note, Warrants or Rights [Table Text Block]	Range of Exercise Price Number Outstanding/Exercisable Weighted Average Remaining Life in Years Weighted Average Exercise Price $5.10 2,500,000 3.37 $ 5.10 $6.45 350,000 3.37 $ 6.45 2,850,000

Note 11 - Business Segment an_2

Note 11 - Business Segment and Geographic Financial Data (Tables)	3 Months Ended
	Mar. 31, 2023
Notes Tables
Schedule of Segment Reporting Information, by Segment [Table Text Block]	Air Pollution FUEL CHEM Three months ended March 31, 2023 Control Segment Segment Other Total Revenues from external customers $ 3,559 $ 3,728 $ — $ 7,287 Cost of sales (2,594 ) (1,888 ) — (4,482 ) Gross margin 965 1,840 — 2,805 Selling, general and administrative — — (3,245 ) (3,245 ) Research and development — — (218 ) (218 ) Operating income (loss) from operations $ 965 $ 1,840 $ (3,463 ) $ (658 ) Air Pollution FUEL CHEM Three months ended March 31, 2022 Control Segment Segment Other Total Revenues from external customers $ 2,204 $ 3,331 $ — $ 5,535 Cost of sales (1,429 ) (1,816 ) — (3,245 ) Gross margin 775 1,515 — 2,290 Selling, general and administrative — — (3,054 ) (3,054 ) Research and development — — (220 ) (220 ) Operating income (loss) from operations $ 775 $ 1,515 $ (3,274 ) $ (984 )
Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas [Table Text Block]	Three Months Ended March 31, 2023 2022 Revenues: United States $ 5,981 $ 3,688 Foreign 1,306 1,847 $ 7,287 $ 5,535 March 31, December 31, 2023 2022 Assets: United States $ 46,893 $ 47,007 Foreign 3,389 3,117 $ 50,282 $ 50,124

Note 12 - Accrued Liabilities (

Note 12 - Accrued Liabilities (Tables)	3 Months Ended
	Mar. 31, 2023
Notes Tables
Other Current Liabilities [Table Text Block]	As of March 31, 2023 December 31, 2022 Contract liabilities (Note 3) $ 427 $ 372 Warranty reserve (Note 13) 159 159 Other accrued liabilities 241 295 Total other accrued liabilities $ 827 $ 826

Note 2 - Summary of Significa_3

Note 2 - Summary of Significant Accounting Policies (Details Textual) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Jun. 30, 2023	Dec. 31, 2022
Investment Plan, Maximum Amount. Approved			$ 20,000
Inventory, Net	$ 509		392
Equipment Contstructed for Resale [Member]
Inventory, Net	207		207
Spare Parts [Member]
Inventory, Net	302		185
In Process Equipment [Member]
Inventory, Net	$ 634		$ 634
Minimum [Member]
Debt Securities, Held-to-maturity, Maturity Term (Month)	3 months
Maximum [Member]
Debt Securities, Held-to-maturity, Maturity Term (Month)	36 months
Asset Pledged as Collateral [Member] | Letter of Credit [Member]
Restricted Cash and Investments		$ 1,921
Asset Pledged as Collateral [Member] | Letter of Credit [Member] | Varying Maturity Dates Expiring No Later Than March 31, 2024 [Member]
Restricted Cash and Investments		1,352
Asset Pledged as Collateral [Member] | Letter of Credit [Member] | Latest Maturity Date No Later Than November 30, 2025 [Member]
Restricted Cash and Investments		$ 569

Note 2 - Summary of Significa_4

Note 2 - Summary of Significant Accounting Policies - Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Mar. 31, 2022
Cash	$ 13,505	$ 34,174
Cash equivalents	2,193	0
Restricted cash and cash equivalents included in current assets	0	1,066
Total cash, cash equivalents, and restricted cash and cash equivalents shown in the Condensed Consolidated Statements of Cash Flows	$ 15,698	$ 35,240

Note 2 - Summary of Significa_5

Note 2 - Summary of Significant Accounting Policies - Amortized Cost to Fair Value of HTM Debt Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Amortized cost	$ 18,121	$ 9,341
Gross unrecognized gains	0	0
Gross unrecognized losses	(148)	(168)
Fair value	$ 17,973	$ 9,173

Note 2 - Summary of Significa_6

Note 2 - Summary of Significant Accounting Policies - Debt Securities by Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Within one year, amortized cost	$ 11,067
Within one year, fair value	11,012
After one year through two years, amortized cost	5,607
After one year through two years, fair value	5,535
After two years through three years, amortized cost	1,447
After two years through three years, fair value	1,426
Amortized cost	18,121	$ 9,341
Fair value	$ 17,973	$ 9,173

Note 2 - Summary of Significa_7

Note 2 - Summary of Significant Accounting Policies - Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2023	Dec. 31, 2022
At January 1, 2022	$ 110	$ 223
Provision charged to expense	0	(19)
(Write-offs) / Recoveries	0	(94)
At December 31, 2022	$ 110	$ 110

Note 3 - Revenue 1 (Details Tex

Note 3 - Revenue 1 (Details Textual) Pure in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2023 USD ($)	Mar. 31, 2022 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Contract with Customer, Liability, Current	$ 427		$ 372	$ 390
Contract with Customer, Liability, Revenue Recognized	$ 359	$ 230
Contract with Customer, Contracts in Progress, Number of Contracts Identified as Loss Contracts	0		0
Revenue, Remaining Performance Obligation, Amount	$ 7,588
Air Pollution Control [Member]
Contract with Customer, Asset, after Allowance for Credit Loss	3,444		$ 3,082	1,277
FUEL CHEM [Member]
Contract with Customer, Asset, after Allowance for Credit Loss	$ 0		$ 0	$ 0

Note 3 - Revenue 2 (Details Tex

Note 3 - Revenue 2 (Details Textual) $ in Thousands	Mar. 31, 2023 USD ($)
Revenue, Remaining Performance Obligation, Amount	$ 7,588
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-04-01
Revenue, Remaining Performance Obligation, Amount	$ 7,277
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period (Month)	12 months

Note 3 - Revenue - Revenues Dis

Note 3 - Revenue - Revenues Disaggregated by Product Technology (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Revenues	$ 7,287	$ 5,535
Air Pollution Control [Member]
Revenues	3,559	2,204
Air Pollution Control [Member] | Technology Solutions [Member]
Revenues	2,982	1,841
Air Pollution Control [Member] | Spare Parts [Member]
Revenues	174	96
Air Pollution Control [Member] | Ancillary Revenue [Member]
Revenues	403	267
FUEL CHEM [Member] | Technology Solutions [Member]
Revenues	$ 3,728	$ 3,331

Note 3 - Revenue - Revenues D_2

Note 3 - Revenue - Revenues Disaggregated by Geography (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Revenues	$ 7,287	$ 5,535
UNITED STATES
Revenues	5,981	3,688
Latin America [Member]
Revenues	0	69
Europe [Member]
Revenues	579	404
Asia [Member]
Revenues	727	1,374
Non-US [Member]
Revenues	$ 1,306	$ 1,847

Note 3 - Revenue - Timing of Re

Note 3 - Revenue - Timing of Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Revenues	$ 7,287	$ 5,535
Transferred at Point in Time [Member]
Revenues	4,305	3,694
Transferred over Time [Member]
Revenues	$ 2,982	$ 1,841

Note 3 - Revenue - Components o

Note 3 - Revenue - Components of Accounts Receivable (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Trade receivables	$ 3,295	$ 4,605
Unbilled receivables	3,444	3,082
Other short-term receivables	126	152
Allowance for credit losses	(110)	(110)	$ (223)
Total accounts receivable	$ 6,755	$ 7,729

Note 4 - Restructuring Activi_3

Note 4 - Restructuring Activities (Details Textual) $ in Thousands	Mar. 31, 2023 USD ($)
CHINA | Backlog [Member]
Restructuring and Related Cost, Expected Cost Remaining	$ 5

Note 4 - Restructuring Activi_4

Note 4 - Restructuring Activities - Charges and Net Assets (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Revenues	$ 7,287	$ 5,535
Net loss	(414)	(998)
Total assets	50,282		$ 50,124
Total liabilities	5,680		5,283
CHINA
Revenues	0	1
Net loss	(20)	$ (13)
Total assets	913		929
Total liabilities	80		79
Total net assets	$ 833		$ 850

Note 5 - Accumulated Other Co_3

Note 5 - Accumulated Other Comprehensive Loss - Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2023	Mar. 31, 2022
Balance		$ 44,841	$ 46,200
Balance		44,602	45,133
AOCI Attributable to Parent [Member]
Balance		(1,728)	(1,604)
Foreign currency translation adjustments (1)	[1]	86	(70)
Balance		$ (1,642)	$ (1,674)
[1]In all periods presented, there were no tax impacts related to rate changes and no amounts were reclassified to earnings.

Note 6 - Treasury Stock (Detail

Note 6 - Treasury Stock (Details Textual) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Treasury Stock, Common, Shares (in shares)	976,006	976,006
Treasury Stock, Common, Value	$ 2,251	$ 2,251

Note 7 - Earnings Per Share (De

Note 7 - Earnings Per Share (Details Textual) - shares	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Weighted Average Equity Awards [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount (in shares)	315,400	346,500
Warrant [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount (in shares)	2,850,000	2,850,000
Incremental Equity Awards [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount (in shares)	266,000	56,000

Note 7 - Earnings Per Share - E

Note 7 - Earnings Per Share - Earnings Per Share (Details) - shares	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Basic weighted-average shares (in shares)	30,296,000	30,267,000
Conversion of unsecured loan notes (in shares)	0	0
Unexercised options and unvested RSUs (in shares)	0	0
Diluted weighted-average shares (in shares)	30,296,000	30,267,000

Note 8 - Stock-based Compensa_3

Note 8 - Stock-based Compensation (Details Textual) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Grants in Period, Gross (in shares)	0
Deferred Compensation Plan for Directors [Member]
Deferred Compensation Arrangement with Individual, Compensation Expense	$ 0	$ 0
The 2014 Long-term Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized (in shares)	5,600,676
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Available for Grant (in shares)	1,799,250
Share-Based Payment Arrangement, Expense, Tax Benefit	$ 0	$ 0
The 2014 Long-term Incentive Plan [Member] | Share-Based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period (Year)	10 years
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Grants in Period, Gross (in shares)	0
The 2014 Long-term Incentive Plan [Member] | Share-Based Payment Arrangement, Option [Member] | Share-Based Payment Arrangement, Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	50%
The 2014 Long-term Incentive Plan [Member] | Share-Based Payment Arrangement, Option [Member] | Share-Based Payment Arrangement, Tranche Two [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	25%
The 2014 Long-term Incentive Plan [Member] | Share-Based Payment Arrangement, Option [Member] | Share-Based Payment Arrangement, Tranche Three [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	25%
The 2014 Long-term Incentive Plan [Member] | Restricted Stock Units (RSUs) [Member]
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount	$ 774
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)	2 years 3 months 7 days
The 2014 Long-term Incentive Plan [Member] | Restricted Stock Units (RSUs) [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year)	2 years
The 2014 Long-term Incentive Plan [Member] | Restricted Stock Units (RSUs) [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year)	4 years

Note 8 - Stock-based Compensa_4

Note 8 - Stock-based Compensation - Stock-based Compensation (Details) - Selling, General and Administrative Expenses [Member] - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Stock options and restricted stock units, net of forfeitures	$ 89	$ 18
After-tax effect of stock-based compensation	$ 89	$ 18

Note 8 - Stock-based Compensa_5

Note 8 - Stock-based Compensation - Stock Option Activity (Details) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2023 USD ($) $ / shares shares
Beginning balance, number of options outstanding (in shares) | shares	384,500
Beginning balance, option, weighted average exercise price (in dollars per share) | $ / shares	$ 2.98
Granted, options (in shares) | shares	0
Granted, option, weighted average exercise price (in dollars per share) | $ / shares	$ 0
Exercised, options (in shares) | shares	0
Exercised, option, weighted average exercise price (in dollars per share) | $ / shares	$ 0
Expired or forfeited, options (in shares) | shares	0
Expired or forfeited, option, weighted average exercise price (in dollars per share) | $ / shares	$ 0
Ending balance, number of options outstanding (in shares) | shares	384,500
Ending balance, option, weighted average exercise price (in dollars per share) | $ / shares	$ 2.98
Outstanding, weighted average remaining contractual term (Year)	2 years 2 months 8 days
Outstanding, aggregate intrinsic value | $	$ 28
Exercisable, options (in shares) | shares	384,500
Exercisable, option, weighted average exercise price (in dollars per share) | $ / shares	$ 2.98
Exercisable, weighted average remaining contractual term (Year)	2 years 2 months 8 days
Exercisable, aggregate intrinsic value | $	$ 28

Note 8 - Stock-based Compensa_6

Note 8 - Stock-based Compensation - Restricted Stock Activity (Details) - Restricted Stock Units (RSUs) [Member]	3 Months Ended
	Mar. 31, 2023 $ / shares shares
Beginning balance, unvested restricted stock units, shares (in shares) | shares	767,048
Beginning balance, unvested restricted stock units, weighted average grant date fair value (in dollars per share) | $ / shares	$ 1.32
Granted, unvested restricted stock units, shares (in shares) | shares	100,000
Granted, unvested restricted stock units, weighted average grant date fair value (in dollars per share) | $ / shares	$ 1.25
Ending balance, unvested restricted stock units, shares (in shares) | shares	867,048
Ending balance, unvested restricted stock units, weighted average grant date fair value (in dollars per share) | $ / shares	$ 1.31

Note 9 - Warrants - Summary of

Note 9 - Warrants - Summary of Warrants Outstanding and Exercisable (Details)	3 Months Ended
	Mar. 31, 2023 $ / shares shares
Number outstanding/ exercisable (in shares)	2,850,000
Warrants Issued in Connection with Private Placement [Member]
Number outstanding/ exercisable (in shares)	2,500,000
Weighted average remaining life (Year)	3 years 4 months 13 days
Weighted average exercise price (in dollars per share) | $ / shares	$ 5.10
The Placement Agent Warrants [Member]
Number outstanding/ exercisable (in shares)	350,000
Weighted average remaining life (Year)	3 years 4 months 13 days
Weighted average exercise price (in dollars per share) | $ / shares	$ 6.45

Note 10 - Debt Financing (Detai

Note 10 - Debt Financing (Details Textual) - USD ($) $ in Thousands	Jun. 30, 2022	Mar. 31, 2023
Percentage of Face Amount of Letters of Credit As Collateral	150%
Payment, Basis Points on Face Value of Letters of Credit	2.50%
Letters of Credit Outstanding, Amount		$ 1,281
Asset Pledged as Collateral [Member]
Investments		$ 1,921

Note 11 - Business Segment an_3

Note 11 - Business Segment and Geographic Financial Data (Details Textual)	3 Months Ended
	Mar. 31, 2023
Number of Reportable Segments	2

Note 11 - Business Segment an_4

Note 11 - Business Segment and Geographic Financial Data - Reporting Segment Net Sales and Gross Margin (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Revenues from external customers	$ 7,287	$ 5,535
Cost of sales	(4,482)	(3,245)
Gross margin	2,805	2,290
Selling, general and administrative	(3,245)	(3,054)
Research and development	(218)	(220)
Operating income (loss) from operations	(658)	(984)
Segment Reconciling Items [Member]
Revenues from external customers	0	0
Cost of sales	0	0
Gross margin	0	0
Selling, general and administrative	(3,245)	(3,054)
Research and development	(218)	(220)
Operating income (loss) from operations	(3,463)	(3,274)
Air Pollution Control [Member]
Revenues from external customers	3,559	2,204
Air Pollution Control [Member] | Operating Segments [Member]
Revenues from external customers	3,559	2,204
Cost of sales	(2,594)	(1,429)
Gross margin	965	775
Selling, general and administrative	0	0
Research and development	0	0
Operating income (loss) from operations	965	775
FUEL CHEM [Member] | Operating Segments [Member]
Revenues from external customers	3,728	3,331
Cost of sales	(1,888)	(1,816)
Gross margin	1,840	1,515
Selling, general and administrative	0	0
Research and development	0	0
Operating income (loss) from operations	$ 1,840	$ 1,515

Note 11 - Business Segment an_5

Note 11 - Business Segment and Geographic Financial Data - Geographic Segment Financial Data (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Revenues	$ 7,287	$ 5,535
Assets	50,282		$ 50,124
UNITED STATES
Revenues	5,981	3,688
Assets	46,893		47,007
Non-US [Member]
Revenues	1,306	$ 1,847
Assets	$ 3,389		$ 3,117

Note 12 - Accrued Liabilities -

Note 12 - Accrued Liabilities - Components of Other Accrued Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Contract liabilities (Note 3)	$ 427	$ 372	$ 390
Warranty reserve (Note 13)	159	159
Other accrued liabilities	241	295
Total other accrued liabilities	$ 827	$ 826

Note 13 - Commitments and Con_2

Note 13 - Commitments and Contingencies (Details Textual) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Standard Product Warranty Accrual, Ending Balance	$ 159	$ 159
Other Accrued Liabilities [Member]
Loss Contingency Accrual, Ending Balance	$ 0	$ 0

Note 14 - Income Taxes (Details

Note 14 - Income Taxes (Details Textual) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Effective Income Tax Rate Reconciliation, Percent	0%	0%
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21%
Unrecognized Tax Benefits	$ 0		$ 0