energies

Article Conventional and Alternative Sources of Thermal Energy in the Production of —An Impact on CO2 Emission

Karolina Wojtacha-Rychter 1, Piotr Kucharski 2 and Adam Smolinski 3,*

1 Department of Mining Aerology, Central Mining Institute, Pl. Gwarków 1, 40-166 Katowice, Poland; [email protected] 2 Department of Environmental Monitoring, Central Mining Institute, Pl. Gwarków 1, 40-166 Katowice, Poland; [email protected] 3 Central Mining Institute, Pl. Gwarków 1, 40-166 Katowice, Poland * Correspondence: [email protected]; Tel.: +48-322-592-252

Abstract: The article evaluates the reduction of carbon dioxide emission due to the partial substitu- tion of with alternative in clinker manufacture. For this purpose, the calculations were performed for seventy waste-derived samples of alternative fuels with variable calorific value and variable share in the mixture. Based on annual clinker production data of the Polish Cement

Association and the laboratory analysis of fuels, it was estimated that the direct net CO2 emissions from fossil fuel alone were 543 Mg of CO2 per hour. By contrast with the full substitution of coal with alternative fuels (including 30% of biomass), the emission ranged from 302 up to 438 Mg

of CO2 per hour, depending on fuel properties. A reduction of 70% in the share of fossil fuels resulted in about a 23% decrease in net emissions. It was proved that the increased use of alternative fuels

 as an additive to the fuel mix is also of economic importance. It was determined that thanks to the  combustion of 70% of alternative fuels of calorific value from 15 to 26 MJ/kg, the hourly financial

Citation: Wojtacha-Rychter, K.; profit gain due to avoided CO2 emission and saved 136 megatons of coal totaled an average of Kucharski, P.; Smolinski, A. 9718 euros. The results confirmed that the co-incineration of waste in cement can be an effective, Conventional and Alternative long-term way to mitigate carbon emissions and to lower clinker production costs. This paper may Sources of Thermal Energy in the constitute a starting point for future research activities and specific case studies in terms of reducing

Production of Cement—An Impact on CO2 emissions. CO2 Emission. Energies 2021, 14, 1539. https://doi.org/10.3390/en14061539 Keywords: alternative fuels; carbon dioxide reduction; financial benefits; cement industry

Academic Editor: Francesco Frusteri

Received: 12 February 2021 1. Introduction Accepted: 8 March 2021 Published: 11 March 2021 Cement manufacturing constitutes a significant source of anthropogenic CO2 emis- sions both in the European Union and in the world [1]. The sector is responsible for

Publisher’s Note: MDPI stays neutral approximately 5–9 percent of worldwide emissions [2,3]. In 2010–2019, carbon dioxide with regard to jurisdictional claims in coming from the Polish cement industry constituted about 2–3% of the country’s total CO2 published maps and institutional affil- emissions [4,5]. Between 2010 and 2016, the CO2 emission in the cement sector remained at iations. an average level of 9.5 million tons, except for the increase to the level of 11.43 million tons in 2011, related to the record results in the construction industry in terms of the number of implemented projects. After 2016, a slow increase in the concentration of carbon dioxide from clinker production was observed, again to the level of 11.29 million tons in 2019,

Copyright: © 2021 by the authors. which was conditioned by economic growth. Based on the annual production of clinker Licensee MDPI, Basel, Switzerland. and cement for this period [5], it can be estimated that circa 700–800 kg of CO2 was emitted This article is an open access article per ton of clinker produced and about 500–700 kg of CO2 per one ton of cement produced. distributed under the terms and In a cement plant, the process plays an important role as concerns the conditions of the Creative Commons environmental impact. It results from the fact that around 50–60% [6] of the CO2 is liberated Attribution (CC BY) license (https:// directly during the reaction of thermal decomposition of . The combustion of creativecommons.org/licenses/by/ fossil fuels in cement kilns contributes to about 40% of the carbon dioxide emissions [7], 4.0/).

Energies 2021, 14, 1539. https://doi.org/10.3390/en14061539 https://www.mdpi.com/journal/energies Energies 2021, 14, 1539 2 of 15

while 10% of the CO2 released comes from indirect emissions due to electrical power consumption, mainly during the grinding of cement and raw materials. According to the EU climate policy, the cement industry is obliged to reduce the level of its CO2 emissions by around 30% until 2030 with the target of reaching net-zero emissions by 2050 [8]. Therefore, improving energy and ecological efficiency currently constitute the industry priority objectives to meet the targets set by the European Union. In recent years, the key activities of the cement industry in terms of sustainable development and the EU requirements concerning the reduction of CO2 emissions have been related to decreasing the use of energy and fossil fuels. The elimination of the wet process and the introduction of the dry method were the first steps taken to achieve energy efficiency. As a result, the modernization of cement plants enabled the reduction of specific heat consumption by almost 30–40%. In the wet process, the raw materials were introduced to the rotary in the form of slurry with a moisture content of about 30–40% [9]. Therefore, the higher energy consumption was caused by the necessity of evaporating water from the raw materials. The specific heat consumption of the wet process exceeds 6 kJ per one kilogram of clinker. In turn, in the dry process, pre-heating and pre-calcining systems were incorporated. Dry kilns with a pre-heater consist of 4–6 vertical cyclones through which the raw meal passes down in the opposite direction of the moving hot exhaust gases [7]. As a consequence, the raw meal is partially pre-heated and pre-calcined. Such a system allowed reducing the unit heat consumption to a level below 4–5 kJ per kg of clinker. The pre-calciner is an additional furnace that calcines the materials after they have passed through the pre-heater but before they enter the rotary kiln. The pre-calciner chamber and the pre-heater account for approximately 40% of the fuel use, while 60% of the fuel is consumed in the rotary kiln. In addition, about 80–90% of the raw meal is calcinated [10]. An improvement of thermal efficiency and the reduction of CO2 emissions in cement production were also achieved by the introduction of new types of cement with the limited share of clinker by the application of industrial by-products, e.g., granulated blast furnace slags or fly ashes as admixtures [11,12]. In 2016, approximately 4 million tons of industrial waste were used for cement manufacturing in Poland. Another effective way to lower production costs and carbon emissions from the clinker production process is the co-combustion of waste in cement kilns [13]. Until the 1980s, coal constituted the main primary energy source in clinker production, with a high emission factor of around 95 kg CO2/GJ (at the calorific value of 22.70 MJ/kg) [14,15]. The reduction of carbon dioxide emissions from fossil fuel combustion in the rotary kiln was achieved by the application of fuels made from waste. Waste-derived fuels include a wide range of refuse materials (i.e., residues from MSW recycling, industrial/trade waste, , biomass waste, etc.) which have been processed to fulfill the guidelines and regulatory or industry specifications, mainly to obtain a high calorific value. Different terms and abbreviations are used for the fuel produced from waste, e.g., in Germany, it is labeled as SBS, EBS, or BRAM, and in Italy as CDR, CSS [16]. In other European countries, the fuel is referred to as an (AF) [17] or refuse-derived fuel (RDF) [18,19], while the European Committee for Standardization adopted the name solid secondary fuel (SRF) [20]. In the present work, the term alternative fuel will be applied to the fuel coming from waste. Alternative fuels are also subject to standard obligations related to CO2 emission monitoring and reporting. However, according to the EU Emissions Trading System, a part of the fuel that constitutes the biogenic (or biodegradable) fraction is treated as CO2-neutral and can be excluded from total emission [21–24]. So, replacing fossil fuels with alternative fuels brings about a number of economic benefits including fuel cost savings and lower fees for carbon dioxide emission. In 2020, Cembureau, the European Cement Association, published a new carbon neutrality roadmap that outlines different routes and options for achieving a significant reduction in CO2 emission [8,25]. According to the report, the future activities of the Polish and European cement industry towards reducing environmental impact and achieving EU Energies 2021, 14, x FOR PEER REVIEW 3 of 15 Energies 2021, 14, 1539 3 of 15

EU goals should focus on the further valorization of waste in the production process (i.e., the usegoals of waste should as an focus alternative on the further fuel and valorization a raw material of waste in clinker in the production). production process (i.e., the Theuse scope of waste of this as work an alternative was to determine fuel and athe raw direct material CO2 emission in clinker from production). co-combustion of the fossil Thefuel scopeand alternative of this work fuels. was From to determine the point the of view direct of CO environmental2 emission from protection, co-combustion this constitutesof the fossil an fuelurgent and issue alternative to be addr fuels.essed. From The the calculations point of view were of environmental performed based protection, on the thisamount constitutes of fuels an needed urgent for issue annual to be clinker addressed. production The calculations data and the were CO performed2 emission based factor ofon the the fuels. amount In the of analyzed fuels needed case, for vari annualous configurations clinker production of fuel dataco-combustion and the CO were2 emission assumed;factor secondly, of the fuels. hard Incoal the and analyzed alternative case, variousfuels were configurations burned only of in fuel the co-combustion main burner were of the rotaryassumed; kiln. secondly, Seventy hard samples coal andof alternative alternative fuels fuels were were analyzed burned only to investigate in the main how burner of the rotary kiln. Seventy samples of alternative fuels were analyzed to investigate how the the quality parameters of various alternative fuels may affect the final amount of CO2 emission.quality The parametersmodified parameters of various alternative of the samples fuels mayincluded affect the the calorific final amount value of and CO2 theemission. carbonThe content. modified In the parameters literature, of the the correl samplesation included between the AF calorific parameters value and thethe carbonamount content. In the literature, the correlation between AF parameters and the amount of CO emissions of CO2 emissions has been poorly discussed. Previously, the researchers [26–28] have2 fo- cused hasprimarily been poorly on studying discussed. the changes Previously, of clinker the researchers reactivity [26 resulting–28] have from focused the primarilyuse of on variousstudying alternative the changesfuels in ofthe clinker production reactivity of cement. resulting In from this the work, use ofan various economic alternative effect fuels in the production of cement. In this work, an economic effect achieved due to avoided CO2 achieved due to avoided CO2 emission and the mass saving of the fossil fuel was addi- emission and the mass saving of the fossil fuel was additionally calculated. tionally calculated. 2. Cement Manufacturing Process 2. Cement Manufacturing Process The worldwide cement production in 2019 reached the level of 4 billion tons, this was Thean worldwide increase of cement approximately production 50% in as 2019 compared reached with the level 2005 of production. 4 billion tons, Until this now, was China an increasehas been of approximately the largest cement 50% as producer compared by with installed 2005 capacityproduction. manufacturing Until now, China over halfhas of the been theworld’s largest cement, cement with producer India as by the insta secondlled globalcapacity producer manufacturing [29]. World over cement half of production the world’sin cement, 2018, by with regions India and as the major second countries, global producer is presented [29]. in World Figure cement1. Since production 2017, Poland in has 2018, bybeen regions the third-largestand major countries, producer is ofpresen cementted in Figure Europe, 1. afterSinceGermany 2017, Poland and has Italy. been Cement the third-largestproduction producer in Poland of cement in 2019 in amounted Europe, after to 19.0 Germany million and tons, Italy. which Cement is 10% produc- more than tion in inPoland 2017. in 2019 amounted to 19.0 million tons, which is 10% more than in 2017.

CEMBUREAU; CIS; 2.60% 6.40% (EU28: 4.4% Oceania; 0.30% Non EU28: 2%) Japan; 1.40% America (without USA); 4.60%

USA; 2.20%

Africa; 5.10%

China; 54.50% Asia (without China, Japan, India); 14.30%

India; 8.20%

Figure 1. World cement production in 2018, by region and main countries. Figure 1. World cement production in 2018, by region and main countries. Cement is a hydraulic binder, which means that after mixing with water it sets, hard- Cementens, and is a achieves hydraulic proper binder, strength which characteristics,means that after even mixing in underwaterwith water it conditions sets, hard-[30,31]. ens, andDue achieves to its properties,proper strength cement characteri is widelystics, used even as in a bindingunderwater material conditions in the [30,31]. construction Due toindustry its properties, performing cement the is widely role of used a component as a binding of material mixtures,in the construction mortars, plasters,indus- and try performingmany other theproducts role of a ofcomponent construction of concrete chemistry. mixtures, This finely mortars, ground plasters, material and of graymany color is other productsproduced of by construction grinding clinker chemistry. with This calcium finely sulfate, ground being material a setting of gray time color regulator is pro- (in the duced formby grinding of gypsum clinker or anhydrite),with calcium and sulfate various, being ingredients a setting time such regulator as granulated (in the blast form furnace of gypsumslag, or fly anhydrite), ash, or limestone and va (dependingrious ingredients on the such type as of granulated cement) in ablast cement furnace mill slag, [32]. fly Portland ash, orclinker limestone is obtained(depending by on burning the type ground of cement) raw materialsin a cement in mill a rotary [32]. Portland kiln. The clinker five stages which can be distinguished in the clinker production process occur in the following order:

Energies 2021, 14, x FOR PEER REVIEW 4 of 15

Energies 2021, 14, 1539 4 of 15 is obtained by burning ground raw materials in a rotary kiln. The five stages which can be distinguished in the clinker production process occur in the following order: (1) the dehy- dration(1) theprocess dehydration (heating process and drying (heating of the and ho dryingmogenized of the raw homogenized materials), raw(2) the materials), calcination (2) the processcalcination (decomposition process (decompositionof raw materials ofinto raw calcium materials oxide into and calcium carbonoxide dioxide and [33,34], carbon (3) diox- the clinkerizationide [33,34], (3) process the clinkerization (formation of process clinker (formation phases: tricalcium of clinker silicate phases: (C tricalcium3S), dicalcium silicate silicate(C3 (CS),2S), dicalcium tricalcium silicate aluminate (C2S), (C tricalcium3A) and tetracalcium aluminate (C aluminoferrite3A) and tetracalcium (C4AF) and aluminoferrite (4) the clinker(C4 coolingAF) and process. (4) the clinkerThe cement cooling manufactur process. Theing cementprocess, manufacturing along with marked process, sources along of with pollutantmarked emissions, sources is of schematically pollutant emissions, displayed is schematicallyin Figure 2 [32]. displayed in Figure2[32].

RAW MATERIAL RAW MEAL

PM PM PM PM

DRYING HOMOGENIZATION QUARRING CRUSHING GRINDING STORAGE

E E E E

CLINKER

PM GAS PM GAS PM GAS

CLINKER CLINKER HEATING PRE-HEATING STORAGE COOLING

E H H

CEMENT

PM PM PM

GRINDING IN CEMENT CEMNET STORAGE PACKING FUEL GRINDING

E E Inputs: Emission: E- electrical energy PM- particular matter E H- thermal energy GAS- gases emission

FigureFigure 2. Flow 2. Flow chart chart of cement of cement manufacturing. manufacturing.

3. Materials3. Materials and andMethods Methods In theIn present the present work, work, 70 alternative 70 alternative fuel fuel(AF) (AF) samples, samples, understood understood as “solid as “solid secondary secondary fuel”fuel” according according to the to EN the 15357: EN 15357:2011 2011 standard standard,, were were analyzed analyzed to determine to determine the potential the potential reductionreduction of direct of direct CO2 COemission2 emission from from the co-firing the co-firing of waste-derived of waste-derived alternative alternative fuels. fuels. SamplesSamples were were derived derived by Cement by Cement Plant, Plant, Poland. Poland. The Thetypes types of fuels of fuels covered covered in the in study the study are mixturesare mixtures of non-hazardous of non-hazardous high-calorie high-calorie waste waste such such as as plastics, plastics, paper, textiles,textiles, andand tires, tires,coming coming from from the the mechanical mechanical treatment treatment of of waste waste (for (for example example sorting, sorting, crushing, crushing, compacting, com- pacting,pelletizing) pelletizing) [17]. [17]. An analysisAn analysis of AF of quality AF quality parameters parameters was was performed performed in the in Departmentthe De- partmentof Environmental of Environmental Monitoring, Monitoring, Central Cent Miningral Institute.Mining Institute. The samples The testedsamples were tested initially weredried initially at the dried temperature at the temperature of 313 K. The of 313 dried K. samplesThe dried were samples ground were with ground the application with the of a applicationknife mill of (LMN-100,a knife mill TESTCHEM); (LMN-100, theTESTCHEM); nominal grain the diameternominal ingrain the prepareddiameter samplein the did preparednot exceed sample 2 mm.did not The exceed test samples 2 mm. wereThe test obtained samples by were grinding obtained with theby grinding use of a cryogenic with the usemill of (6870, a cryogenic SPEX SamplePrep mill (6870, SPEX LLC, Sa Metuchen,mplePrep NJ, LLC, USA). Metuchen, The total NJ, carbon USA). content The total in the carbonsamples content was in determinedthe samples by was means determin of theed high-temperature by means of the combustionhigh-temperature method com- with IR bustiondetection method (HELIOS with IR CHSdetection 900, ELTRA),(HELIOS inCHS accordance 900, ELTRA), with in standard accordance EN 15407:2011.with stand- The calorific value and the heat of combustion were determined using the calorimetric method ard EN 15407:2011. The calorific value and the heat of combustion were determined using (C 5000 IKA WERKE), based on the PN-EN 15400:2011 standard. The results of the tests of AF samples are presented in Figure3.

Energies 2021, 14, x FOR PEER REVIEW 5 of 15

Energies 2021, 14, 1539 5 of 15 the calorimetric method (C 5000 IKA WERKE), based on the PN-EN 15400: 2011 standard. The results of the tests of AF samples are presented in Figure 3.

26 100 calorific value 24 carbon content 90 22 80 20 18 70 16 60 14 50 12 40 10 wt.% Carbon content, Calorific value, MJ/kg value, Calorific 8 30 6 20 4 2 10 0 0 1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67 70

Sample number

Figure 3. Parameters of alternative fuels. Figure 3. Parameters of alternative fuels.

The total emission of CO2 coming from the co-combustion of coal and alternative fuels in a cementThe total kiln emission was calculated of CO2 using coming the from following the co-combustion equation [35]: of coal and alternative fuels in a was calculated using the following equation [35]: = · ECO2, f uel Z EFCO2 (1) 𝐸, =𝑍∙𝐸𝐹 (1) where: E 2 2 CO2, 𝐸f uel,is CO is2 COemission emission from from the the combustion combustion process process by by type type of of fuel fuel in in Mg Mg CO CO2 per per hour; hour; Z is the𝑍 is amount the amount of fuel of combusted fuel combusted mass converted mass converted into the energyinto the content energy of content this fuel of in this TJ perfuel hour; in TJ per hour; EF 2 2 CO2𝐸𝐹is the is CO the2 COemission emission factor factor in Mg inCO Mg2 /TJ.CO /TJ. TheThe carboncarbon dioxidedioxide emissionemission factorfactor fromfrom fuelfuel combustioncombustion expressedexpressed inin megatonsmegatons ofof COCO22 emittedemitted perper unitunit ofof calorificcalorific valuevalue isis calculatedcalculated accordingaccording toto equationequation[ [35]:35]:

=3.664 3.664·C ∙ 𝐶 EF𝐸𝐹= (2)(2) CO2 Q𝑄 where: where: 2 2 𝐸𝐹 is the CO emission factor in Mg CO /TJ; EFCO is the CO2 emission factor in Mg CO2/TJ; 23.664 is a molecular weight ratio of CO2 to C; 3.664 is a molecular weight ratio of CO to C; 𝐶 is carbon content of combusted2 fuel in %; C is carbon content of combusted fuel in %; 𝑄 is calorific value in TJ/Mg. Q is calorific value in TJ/Mg. The total emission from the combustion process was a sum of CO2 emissions from all fuelsThe used, total i.e., emission from coal from and the alternative combustion fuels. process was a sum of CO2 emissions from all fuels used,The calculation i.e., from coalwas and performed alternative for fuels.several scenarios with various shares of alterna- tive Thefuels. calculation The fuel mix was compositio performedn for data several are presented scenarios within Table various 1. shares of alternative fuels. The fuel mix composition data are presented in Table1. Table 1. Share of energy coming from conventional and alternative sources. Table 1. Share of energy coming from conventional and alternative sources. Options Fuel Type 1 2 Options3 4 5 6 7 8 9 10 11 Fuel Type 1 2Coal 3 4100% 590% 80% 6 70% 760% 50% 8 40% 30% 9 20% 10 10% 110% Alternative fuel 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Coal 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Alternative fuel 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% For the purpose of this work, the following assumptions were made as listed below:

Energies 2021, 14, 1539 6 of 15 Energies 2021, 14, x FOR PEER REVIEW 6 of 15

For the purpose of this work, the following assumptions were made as listed below: (a) The yearly average heat demand for the production of clinker equals 45 × 109 MJ. (a) The yearly average heat demand for the production of clinker equals 45 × 109 MJ. The value was calculated from the annual clinker production data for the period of 2010– The value was calculated from the annual clinker production data for the period of 2010– 2018, published in the Polish Cement Association report [4], and using the following 2018, published in the Polish Cement Association report [4], and using the following Equation (3): Equation (3):

H𝐻d ==𝑀Mc·H∙𝐻s (3)(3) where:where: 𝐻 2 Hd is the is average the average CO2 totalCO heattotal demandheat demand to produce to produce clinker clinker in MJ in per MJ year; per year; Mc is𝑀 average is average capacity capacity of cement of cement kiln in kiln Mg in per Mg year; per year; Hs is𝐻 specific is specific heat consumptionheat consumption per ton per of ton clinker of clinker in MJ/Mg. in MJ/Mg. TheThe resultsresults ofof thethe PolishPolish CementCement AssociationAssociation reportreport areare summarizedsummarized inin FigureFigure4 .4. As As seen,seen, thethe specificspecific heatheat consumptionconsumption perper tonton ofof clinkerclinker rangedranged fromfrom 36773677 toto 38283828 MJ/Mg. MJ/Mg. 6 Thus,Thus, itit waswas calculatedcalculated thatthat withwith an an average average capacity capacity of of cement cement kiln kiln of of about about 12 12× ×10 106 MgMg 9 ofof clinker,clinker, itit isis necessarynecessary toto provideprovide approximatelyapproximately 44–4644–46× × 109 MJMJ of of heat. heat.

Total mass of clinker 4000 16 Mg

3500 14 6 3000 12 2500 10 2000 8 1500 6 1000 4 500 2 ton MJ/Mg of clinker,

0 0 of clinker,Total mass 10 Specific heat consumption per 2010 2011 2012 2013 2014 2015 2016 2017

Year FigureFigure 4.4. ClinkerClinker productionproduction datadata forfor thethe periodperiod ofof 2010–2018,2010–2018, Poland.Poland.

(b)(b) TheThe rotaryrotary kilnkiln isis operatedoperated forfor aboutabout 80008000 hh annually.annually. (c)(c) TheThe fuelfuel mixmix isis combustedcombusted onlyonly inin thethe mainmain burner.burner. (d)(d) TheThe calorificcalorific valuevalue andand thethe carboncarbon contentcontent ofof coalcoal areare 28.8128.81 MJ/kg MJ/kg andand 76.2%wt.,76.2%wt., respectivelyrespectively [[36].36]. TheThe qualityquality parametersparameters ofof coalcoal areare unchangedunchanged inin thethe calculations.calculations. (e)(e) TheThe qualityquality parametersparameters ofof alternativealternative fuelsfuels (i.e.,(i.e., calorificcalorific valuevalue and carbon content) areare notnot constant.constant. TheThe calorificcalorific valuevalue ofof AFAF samplessamples testedtested variesvaries withinwithin aa comparativelycomparatively widewide range,range, fromfrom thethe highesthighest valuevalue of of about about 25.58 25.58 MJ/kg MJ/kg toto thethe lowestlowest oneone ofof 15.0215.02 MJ/kg.MJ/kg. (f)(f) InIn thethe performed performed calculation, calculation, it it was was assumed assumed that that the the biogenic biogenic fraction fraction in alternative in alterna- fuel samples will be 30% [37,38]. tive fuel samples will be 30% [37,38]. −1 (g) The price of CO2 emission allowances is 30.04 €·Mg [39]. (g) The price of CO2 emission allowances is 30.04 €∙Mg−1 [39]. 4. Results and Discussion 4. Results and Discussion 4.1. Alternative Fuels Characteristic 4.1. Alternative Fuels Characteristic The results of the qualitative analysis (see Figure3) indicate differences between indi- vidualThe samples results of of alternative the qualitative fuel, whichanalysis may (see result Figure from 3) indicate the heterogeneous differences composition between in- ofdividual the waste samples stream of used alternative for fuel fuel, production. which may Alternative result from fuels the are heterogeneous mainly produced composi- from mixedtion of streamsthe waste of municipalstream used solid for waste,fuel prod includinguction. differentAlternative shares fuels of are plastic, mainly paper, produced textile, orfrom rubber. mixed A streams typical compositionof municipal ofsolid AF waste, regarding including its different different components shares of plastic, is presented paper, intextile, works or [ 20rubber.,40–42 A]. Thetypical selected composition groups of AF wastes regarding are characterized its different by components various physical- is pre- chemicalsented in parametersworks [20,40–42]. [43,44]. The Plastics selected have groups a very of high wastes calorific are characterized value, even by exceeding various 40physical-chemical MJ/kg, due to a lowparameters content of[43,44]. ash and Plastics moisture, have while a very paper high and calorific wood hasvalue, the even calorific ex- valueceeding of about40 MJ/kg, 11–20 due MJ/kg. to a low For content comparison, of ash the and heating moisture, value while of coal paper is about and 28wood MJ/kg. has Thethe calorific share of value a given of fractionabout 11–20 in the MJ/kg. alternative For comparison, fuel determines the heating its calorific value value. of coal is about 28 MJ/kg. The share of a given fraction in the alternative fuel determines its calorific value.

Energies 2021, 14, 1539 7 of 15 Energies 2021, 14, x FOR PEER REVIEW 7 of 15

The calorific value of the tested AF samples ranges from 15.02 MJ/kg to 25.58 MJ/kg, The calorific value of the tested AF samples ranges from 15.02 MJ/kg to 25.58 MJ/kg, while the carbon content changes from 37.09% to 64.42%. The average carbon content while the carbon content changes from 37.09% to 64.42%. The average carbon content in the in the alternative fuels with the following calorific values: 15–16 MJ/kg, 16–17 MJ/kg, alternative fuels with the following calorific values: 15–16 MJ/kg, 16–17 MJ/kg, 17–18 MJ/kg, 17–18 MJ/kg, 18–19 MJ/kg, 19–20 MJ/kg, 20–21 MJ/kg, 21–22 MJ/kg, 22–23 MJ/kg, 18–1923–24 MJ/kg, MJ/kg ,19–20 24–25 MJ/kg, MJ/kg, 20–21 and 25–26 MJ/kg, MJ/kg 21–22 is MJ/kg, equal to22–23 38.49%, MJ/kg, 42.70%, 23–24 45.57%, MJ/kg, 48.66%, 24–25 MJ/kg,51.64%, and 52.63%, 25–26 53.18%,MJ/kg is 53.23%,equal to 54.65%,38.49%, 54.83%,42.70%, 45.57%, and 60.51%, 48.66%, respectively. 51.64%, 52.63%, As shown 53.18%, in 53.23%,Figure3 ,54.65%, the higher 54.83%, carbon and content 60.51%, in respectively. individual AFAs samplesshown in does Figure not 3, always the higher correspond carbon contentwith a higherin individual calorific AF value.samples For does example, not alwa theys correspond carbon content with ina higher sample calorific 18 (with value. the Forcalorific example, value the of 18.12carbon MJ/kg) content is in about sample 55.24%, 18 (with andin the samples calorific 67 value (with of the 18.12 calorific MJ/kg) value is aboutof 24.87 55.24%, MJ/kg) and and in samples 68 (with 67 the (with calorific the calorific value ofvalue 25.07 of MJ/kg)24.87 MJ/kg) the carbon and 68 content(with the is calorific52.38% andvalue 59.11%, of 25.07 respectively. MJ/kg) the carbon content is 52.38% and 59.11%, respectively.

4.2.4.2. Mass Mass Balance Balance in in Co-Combustion Co-Combustion of of Coal Coal and and Alternative Alternative Fuel Fuel TheThe analyzed analyzed case case demonstrated demonstrated that that for for th thee production production of of 12 12 thousand thousand Mg Mg of of clinker perper year, year, with with a a unit unit heat heat consumption consumption of of 3732 3732 MJ/Mg, MJ/Mg, an anamount amount of 194.31 of 194.31 Mg Mgof coal of coalper hourper hour is needed. is needed. Figure Figure 5 shows5 shows the thequantity quantity of alternative of alternative fuel fuel necessary necessary to obtain to obtain the there- quiredrequired amount amount of ofheat, heat, i.e., i.e., about about 5.6 5.6 TJ TJper per ho hour,ur, with with varying varying levels levels of ofcoal coal substitution. substitution.

400 10% 20% 350 30% 300 40% 250 50% 200 60% 70% 150 80% Mass of AF, Mg/h 100 90% 50 100% 0 15 16 17 18 19 20 21 22 23 24 25 Calorific value of AF, MJ/kg

FigureFigure 5. 5. TheThe mass mass of of the the alternative alternative fuel fuel is is required required for for the the production production of of clinker. clinker. The The substitution substitution ofof coal coal with with alternative alternative fuels fuels was: was: 10%, 10%, 20%, 20%, 30%, 30%, 40%, 40%, 50%, 50%, 60%, 60%, 70%, 70%, 80%, 80%, 90%, 90%, and and 100%. 100%.

AsAs can can be be seen seen in in Figure Figure 55,, anan hourlyhourly demanddemand forfor alternativealternative fuelsfuels decreasesdecreases withwith thethe increaseincrease in in calorific calorific value. value. Assuming Assuming complete complete substitution substitution of of coal coal with with the the fuel fuel of of the the AF AF type,type, the the necessary necessary amount amount of of an alternative fu fuelel with a calorificcalorific valuevalue ofof 15–1915–19 MJ/kgMJ/kg is 300–400300–400 Mg/h, Mg/h, while while for for an an alternative alternative fuel fuel with with a calorific a calorific value value of 19–26 of 19–26 MJ/kg—it MJ/kg—it is 200– is 300200–300 Mg/h. Mg/h. The effect The effectof calorific of calorific value on value the onam theount amount of the alternative of the alternative fuel consumed fuel consumed is less noticeableis less noticeable at the consumption at the consumption of 70–80% of 70–80% coal in the coal clinker in the clinkerproduction. production. For example, For example, at 20% co-combustionat 20% co-combustion of AF, the of difference AF, the difference between the between amount the of amountthe low calorie of the and low high-calorie calorie and fuelshigh-calorie is 31 Mg/h, fuels while is 31 at Mg/h, 80% substitution while at 80% by substitutionAF the difference by AF is the123 differenceMg/h. It was is 123calculated Mg/h. It was calculated that the thermal deficit due to the reduction of coal burning to 40% makes that the thermal deficit due to the reduction of coal burning to 40% makes that 2–3 times that 2–3 times more alternative fuel must be mass transported into the rotary kiln than in more alternative fuel must be mass transported into the rotary kiln than in the case of the the case of the conventional fuel, while with a 20% reduction it is 5–8 times more. This conventional fuel, while with a 20% reduction it is 5–8 times more. This indicates that the indicates that the alternative fuel storage area must be located significantly higher or the alternative fuel storage area must be located significantly higher or the frequency of fuel frequency of fuel supply increased as compared to coal. supply increased as compared to coal. In this study, the mass savings of coal achieved due to a partial replacement with In this study, the mass savings of coal achieved due to a partial replacement with alternative fuel are presented in Table2. Based on the results, it can be estimated that alternative fuel are presented in Table 2. Based on the results, it can be estimated that the the substitution of coal with alternative fuels at the level of 70% means that the savings substitution of coal with alternative fuels at the level of 70% means that the savings for for the cement producer may exceed 55 million euros per year. It should be noted that to the cement producer may exceed 55 million euros per year. It should be noted that to calculate the total financial profit, it is necessary to deduct the costs of alternative fuel from calculate the total financial profit, it is necessary to deduct the costs of alternative fuel the value given in Table2. The price of alternative fuels is much lower compared to the fromcosts the associated value given with in coal, Table which 2. The makes price these of alternative fuels more fuels cost-effective is much lower [45,46 compared]. to the costs associated with coal, which makes these fuels more cost-effective [45,46].

EnergiesEnergies 20212021,, 1414,, x 1539 FOR PEER REVIEW 88 of of 15 15

TableTable 2. 2. EconomicEconomic benefits benefits of of substituting substituting coal coal with with alternative alternative fuel (AF). Mass Saving of the Coal Cost Savings Share of Heat from AF Fuels Mass Saving of the Coal Cost Savings Share of Heat from AF Fuels Mg∙h−1 €∙h−1 −1 −1 10% 19.43Mg ·h 923€· h 20%10% 38.86 19.43 1847 923 30%20% 58.29 38.86 2770 1847 40%30% 77.72 58.29 3693 2770 50%40% 97.15 77.72 4617 3693 60%50% 116.58 97.15 5540 4617 60% 116.58 5540 70% 136.02 6463 70% 136.02 6463 80%80% 155.45 155.45 7387 7387 90%90% 174.88 174.88 8310 8310

4.3. CO2 Emission Balance 4.3. CO2 Emission Balance According to Equation (2) and qualitative data of coal sample (see Section 3) the CO2 According to Equation (2) and qualitative data of coal sample (see Section3) the CO 2 emissionemission factor factor of of coal coal was was calculated calculated as as 3.664 ∙ 0.762 Mg CO · Mg CO 𝐸𝐹 =3.664 0.762 = 96.94 2 (4) EFCO = 0.0288 = 96.94 TJ (4) 2 0.0288 TJ The emission factor for all AF samples tested was calculated in a similar way, the re- The emission factor for all AF samples tested was calculated in a similar way, the sults are summarized in Figure 6. The determined factor values of alternative fuel ranged results are summarized in Figure6. The determined factor values of alternative fuel ranged from 77.22 MgCO2/TJ to 111.78 MgCO2/TJ (the average value being 91.91 MgCO2/TJ). Un- from 77.22 Mg CO2/TJ to 111.78 Mg CO2/TJ (the average value being 91.91 Mg CO2/TJ). certainty estimates for CO2 emission factors for the fossil fuel and alternative fuels were 1.5% Uncertainty estimates for CO emission factors for the fossil fuel and alternative fuels and 3–4%, respectively. As can 2be seen, the factor value of some AF samples exceeds the were 1.5% and 3–4%, respectively. As can be seen, the factor value of some AF samples emission factor from the combustion of coal. Higher emission factor values were recorded exceeds the emission factor from the combustion of coal. Higher emission factor values for sixteen fuel samples (numbered 8, 11, 13, 18, 21, 22, 25, 28, 29, 30, 32, 33, 35, 36, 42, and were recorded for sixteen fuel samples (numbered 8, 11, 13, 18, 21, 22, 25, 28, 29, 30, 32, 33, 50), mainly with a low calorific value of below 20 MJ/kg and a high carbon content (>52%). 35, 36, 42, and 50), mainly with a low calorific value of below 20 MJ/kg and a high carbon Thecontent ratio (>52%).of carbon The content ratio ofand carbon calorific content value and varied calorific from value26.93 variedto 30.49 from for these 26.93 selected to 30.49 samplesfor these of selected AF, while samples for coal of AF, it was while 26.47. for coalAcco itrding was 26.47. to [10], According the emission to [10 factor], the emissionfor hard coalfactor (for for the hard year coal 2019), (for calculated the year based 2019), on calculated the national based average on the calorific national value, average is 94.70, calorific i.e., thevalue, ratio is of 94.70, carbon i.e., to the the ratio calorific of carbon value tois 25. the85. calorific This means value that is 25.85. the most This effective means thatway theto achieve a low CO2 emission factor will be to use alternative fuels with a ratio value below most effective way to achieve a low CO2 emission factor will be to use alternative fuels 25–26.with a ratio value below 25–26.

120 111.78 120 110 110

100 100 . /TJ wt 2 90 90 80 89.96 80 70 70 60 55.24 60 50 50 40 40 45.13 emission factor of coal % Carbon content, 30 30 emission factor of AF

Emission factor, Mg CO Emission factor, 20 20 10 carbon content of AF 10 0 0 15 16 17 18 19 20 21 22 23 24 25 Calorific value of AF, MJ/kg

Figure 6. CO2 emission factor of alternative fuel samples tested. Figure 6. CO2 emission factor of alternative fuel samples tested.

Figure7 illustrates the avoided emission of CO 2 resulting from the co-combustion of coalFigure with 30% 7 illustrates biogenic the carbon-containing avoided emission alternative of CO2 resulting fuels. According from the co-combustion to the data ofthe of coalPolish with Cement 30% biogenic Association, carbon-containing the content of alte biomassrnative in fuels. alternative According fuels to burned the data in Polishof the cement plants in 2008–2016 ranged from 25 to 36% [47].

Energies 2021, 14, x FOR PEER REVIEW 9 of 15

Energies 2021, 14, 1539 9 of 15 Polish Cement Association, the content of biomass in alternative fuels burned in Polish cement plants in 2008–2016 ranged from 25 to 36% [47].

200

-1 180 160 10% of AF , Mg∙h 2 140 20% of AF 30% of AF 120 40% of AF 100 50% of AF 60% of AF 80 70% of AF 60 80% of AF 40 90% of AF 100 of AF 20 Avoided emission of CO 0 0 2 4 6 8 10 12 14 1618 20 2224 26 2830 32 34 3638 40 4244 46 4850 52 54 5658 60 6264 66 6870

Sample number

Figure 7. Avoided CO2 emission from biomass fraction. Figure 7. Avoided CO2 emission from biomass fraction.

Biogenic carbonBiogenic emission carbon comes emission from the comes wast frome of biological the waste origins of biological such originsas residues such as residues or or waste streamswaste from streams forestry from and forestry timber proc andessing, timber processing,agriculture, agriculture,pulp, and paper pulp, as and well paper as well as as sugar industriessugar [45,48]. industries The [biogenic45,48]. The fraction biogenic in a fractiongiven fuel in ais givendetermined fuel is determinedby appropri- by appropriate ate laboratory testslaboratory specified tests in specified European in stan Europeandards, standards,i.e., the manual i.e., the sorting manual method sorting (MS), method (MS), the the selective dissolutionselective dissolution method (SDM), method or th (SDM),e radiocarbon or the radiocarbon method (14C-Method) method (14C-Method) [21,40]. [21,40]. In accordance Inwith accordance the Intergovernmental with the Intergovernmental Panel on Climate Panel Change on Climate guidelines, Change the guidelines, the emission of biogenicemission carbon of biogenic in the form carbon of ca inrbon the formdioxide of carbonfrom the dioxide incineration from theprocess incineration is process regarded as climate-neutralis regarded as since climate-neutral carbon is ge sincenerated carbon by the is generatednatural cycle, by theand natural can be ex- cycle, and can be cluded from theexcluded total amount from theof CO total2 emissions amount of [49,50]. CO2 emissions The majority [49,50 of]. case The studies majority as- of case studies sumed that theassumed amount thatof CO the2 absorbed amount of by CO growing2 absorbed forest bys growing through foreststhe photo-synthesis through the photo-synthesis process is equalprocess to the isemission equal to from the emissionthe comb fromustion the process combustion [51,52]. process However, [51, 52in]. recent However, in recent years, there hasyears, been there a more has and been more a more commo andn more belief common that biomass belief fuels that biomassshould not fuels be should not be considered carbonconsidered neutral carbon when neutralforest energy when resource forest energy management resource is management not carried isout not carried out sustainably [53–55].sustainably In this [work,53–55 ].it was In this assumed work, that it was carbon assumed dioxide that emissions carbon dioxidefrom bio- emissions from mass fraction canbiomass be cons fractionidered can carbon be considered neutral. carbon neutral. As can be seenAs in Figure can be seen7, a co-firing in Figure of7, coal a co-firing with 30% of coalof alternative with 30% fuels of alternative allows one fuels allows one to avoid about 40–59 Mg of CO emission per hour, while with 80% and 100% of AF even to avoid about 40–59 Mg of CO2 emission per 2hour, while with 80% and 100% of AF even 104–150 Mg of CO or 130–188 Mg of CO per hour, respectively. The curves show slight 104–150 Mg of CO2 or 130–188 Mg2 of CO2 per hour, respectively.2 The curves show slight decreases in thedecreases amount inof theavoided amount emission of avoided with emissionthe increases with in the calorific increases value in calorificof the value of the alternative fuelalternative samples (the fuel samples samples are (the number samplesed arefrom numbered the lowest from to the the highest lowest calorific to the highest calorific value), particularlyvalue), with particularly high coal withto AF high subs coaltitution. to AF It substitution. can be related It canto the be fact related that to a the fact that a necessary amountnecessary of a high-calorific amount of a AF high-calorific to supplement AF to the supplement thermal deficit the thermal is lower deficit than is lower than that of a low-calorific fuel. The irregular trend of the curves and the occurrence of peaks that of a low-calorific fuel. The irregular trend of the curves and the occurrence of peaks are related to the variability of quality parameters in the analyzed fuel samples, especially are related to the variability of quality parameters in the analyzed fuel samples, especially the carbon content. For example, the carbon content of fuels with a calorific value of about the carbon content. For example, the carbon content of fuels with a calorific value of about 18 MJ/kg varies from 39.17% to 55.36%. 18 MJ/kg varies from 39.17% to 55.36%. Table3 shows the financial benefits resulting from the avoided fees for CO 2 emissions. Table 3 shows the financial benefits resulting from the avoided fees for CO2 emis- In the analyzed case, the cost of CO2 avoided ranges from 465 euros per hour for the sions. In the analyzed case, the cost of CO2 avoided ranges from 465 euros per hour for lowest reduction of coal combusted to 4185 euros per hour (assuming 90% combustion the lowest reduction of coal combusted to 4185 euros per hour (assuming 90% combustion of the alternative fuel). On an annual basis, these costs will amount to several million of the alternative fuel). On an annual basis, these costs will amount to several million eu- euros. Of course, the greater the biogenic fraction share is, the greater the profit. With the ros. Of course, the greater the biogenic fraction share is, the greater the profit. With the share of the biogenic fraction at the level of 60%, the savings in Table3 will double. The share of the biogenicfinancial fraction benefits at willthe level also dependof 60%, onthe the savings price ofin carbonTable 3 dioxidewill double. emission The allowances of financial benefitsthe will Emission also depend Trading on System the price (EU of ETS) carbon [39 dioxide]. From emission the beginning allowances of 2020 of to mid-March, the Emission Trading System (EU ETS) [39]. From the beginning of 2020 to mid-March, the prices for the emission of 1 Mg of CO2 were at the level of 22–26 euros. At the end of the prices for the emission of 1 Mg of CO2 were at the level of 22–26 euros. At the end of March 2020, the prices of CO2 emission allowances dropped significantly, even to 14 euros. Currently, the exchange price of CO2 emission allowances reaches the level of 28–30 euros.

Energies 2021, 14, 1539 10 of 15

In the analyzed case, each increase in the share of heat from alternative fuels by 10% means on average about 15 Mg per hour of additional CO2 emissions avoided.

Table 3. The financial benefits resulting from the avoided fees for CO2 emissions.

Avoiding CO2 Emission Benefits of Fees from Avoided Share of Heat from (30% of Biomass) Emission of CO2 AF Fuels −1 −1 −1 Mg CO2·h €·h €·year 10% 15.48 465 3,720,268 20% 30.96 930 7,440,536 30% 46.44 1395 11,160,804 40% 61.92 1860 14,881,072 50% 77.40 2325 18,601,341 60% 92.88 2790 22,321,609 70% 108.36 3255 26,041,877 80% 123.84 3720 29,762,145 90% 139.32 4185 33,482,413 100% 154.80 4650 37,202,681

Figure8 presents the total gross and net emissions of CO 2. The gross emission is related to the Mg of CO2 emitted from coal and the alternative fuel together, while net emission takes into account a zero-emission factor from the biodegradable fraction in AF. The calculations were made on the assumption of two different biogenic fraction contents in fuels, namely 30% and 60%. The higher content of the biogenic fraction was assumed based on the results of fuel characteristics from various cement plants, presented in work [20,21]. The mean gross emission factor, at the 10% alternative fuels share in the mix, was 540.21 Mg CO2 per hour, and at the 90% alternative fuels share—it declined to the level of 518.71 Mg CO2 per hour. Uncertainty estimates for the emissions measurement of gross carbon dioxide were on the order of 4–5%. For comparison, to obtain 5.6 TJ·h−1 of heat, 194.31 Mg of coal per hour is needed, which corresponds to the total emission from coal combustion of about 542.90 Mg CO2. As can be observed in Figure8, the replacement of coal with AF has undoubtedly resulted in a reduction of fuel emissions, particularly when the emission from biogenic fraction was considered carbon neutral. It means that the use of biomass and biomass by-products as alternative fuels can be classified as limiting CO2 emission. The mean net emission factor ranged from 524.73 Mg CO2 per hour up to 379.38 Mg CO2 per hour. It was found that each successive 10% increase in the share of heat from alternative fuels (with the biogenic fraction of 30%) contributed to the reduction of the net emission level by each subsequent 3–4%, in relation to the emission from the combustion of coal alone. In the case of 90% coal and 10% alternative fuels, the average level of net emissions from all samples is 524.73 Mg CO2, and with 80% coal and 20% alternative fuels it is 506.56 Mg CO2, whereas with 70% coal and 30% alternative fuels it is 488.39 Mg CO2. With regard to alternative fuels with a twice higher share of the biogenic fraction, each 10% replacement of coal will reduce emissions by about 6%, compared to coal emission. With the lowest share of alternative fuels (10%), the net emission varied from 505.90 Mg CO2 per hour to 513.64 Mg CO2 per hour, while with the higher share of alternative fuels (90%), the minimum net emission was 209.91 Mg CO2 per hour and the maximum was 279.56 Mg CO2 per hour. Based on the results, it was found that with the full substitution of coal, the average gross emission of CO2 from all samples is 30% higher than the net emission (Figure8j), while with 20% substitution of coal the difference is 6% (Figure8b). Energies 2021, 14, x FOR PEER REVIEW 11 of 15 Energies 2021, 14, 1539 11 of 15

Energies 2021, 14, x FOR PEER REVIEW 12 of 15

Figure 8. The amount of CO emitted from co-combustion of coal with (a) 10%, (b) 20%, (c) 30%, (d) 40%, (e) 50%, (f) 60%, Figure 8. The amount of CO2 2 emitted from co-combustion of coal with (a) 10%, (b) 20%, (c) 30%, (d) 40%, (e) 50%, (f) 60%, (g) 70%,(g) 70%, (h) ( 80%,h) 80%, (i) ( 90,i) 90, and and (j) ( 100%j) 100% alternative alternative fuel. fuel.

According to the methodology used for EU-ETS benchmarks, a limit value for clinker production is 766 kg CO2 per Mg clinker [56]. Based on the results shown in Figure 8, gross fuel emission is on average at the level of 353 kg CO2 per Mg of clinker (with the produc- tion of 12 million Mg of clinker per year and the working time of 8000 h). Substitution of 50% and 70% coal with alternative fuels of 30% biomass content resulted in the reduction of fuel emissions to the level of 301 kg CO2 and 277 kg CO2 per Mg of clinker (net emis- sion), respectively. This is about 30–40% of the emission benchmark of 766 kg CO2 per Mg of clinker. It means that approximately 60–70% of CO2 emissions can come from the calci- nation process (process emission). A slight decline of the total net emissions is observed with the increase in the calorific value of the alternative fuels, particularly at the high level of coal substitution with AF (Figure 8h–j). For example, in the case of a 70% share of alternative fuels with the emission factors below 96 Mg CO2/TJ (Figure 6), the average net CO2 emission from samples with a calorific value of 16–17 MJ/kg is 413 Mg CO2/hour, while for samples with a higher calo- rific value in the range of 21–22 MJ/kg and 24–25 MJ/kg, the emissions are 407 Mg CO2/h and 386 Mg CO2/h, respectively. For the sixteen remaining samples with the emission fac- tor above 96 Mg CO2/TJ, the net emission was in the range of 430–470 Mg CO2/h and was only about 13–23% lower than the emission coming from 100% coal combustion, regard- less of the calorific value.

5. Conclusions The paper discusses the issue of using alternative fuels in clinker burning systems. The performed calculations showed the environmental and financial benefits of using al- ternative fuels as coal substitutes in cement manufacturing. The estimated emissions were determined using the CO2 emission factor for coal of 96.43 Mg CO2. The calculation reveals that the net emission of CO2 was reduced by about 25%, which was achieved by the co-combustion of 70% alternative fuels with a CO2 emis- sion factor below 96.43 Mg CO2. In the case of fuel samples with a CO2 emission factor above 96.43 MgCO2, the decline in emissions was slight, about 18%. In the analyzed case,

Energies 2021, 14, 1539 12 of 15

According to the methodology used for EU-ETS benchmarks, a limit value for clinker production is 766 kg CO2 per Mg clinker [56]. Based on the results shown in Figure8 , gross fuel emission is on average at the level of 353 kg CO2 per Mg of clinker (with the production of 12 million Mg of clinker per year and the working time of 8000 h). Substitution of 50% and 70% coal with alternative fuels of 30% biomass content resulted in the reduction of fuel emissions to the level of 301 kg CO2 and 277 kg CO2 per Mg of clinker (net emission), respectively. This is about 30–40% of the emission benchmark of 766 kg CO2 per Mg of clinker. It means that approximately 60–70% of CO2 emissions can come from the calcination process (process emission). A slight decline of the total net emissions is observed with the increase in the calorific value of the alternative fuels, particularly at the high level of coal substitution with AF (Figure8h–j). For example, in the case of a 70% share of alternative fuels with the emission factors below 96 Mg CO2/TJ (Figure6), the average net CO 2 emission from samples with a calorific value of 16–17 MJ/kg is 413 Mg CO2/hour, while for samples with a higher calorific value in the range of 21–22 MJ/kg and 24–25 MJ/kg, the emissions are 407 Mg CO2/h and 386 Mg CO2/h, respectively. For the sixteen remaining samples with the emission factor above 96 Mg CO2/TJ, the net emission was in the range of 430–470 Mg CO2/h and was only about 13–23% lower than the emission coming from 100% coal combustion, regardless of the calorific value.

5. Conclusions The paper discusses the issue of using alternative fuels in clinker burning systems. The performed calculations showed the environmental and financial benefits of using alternative fuels as coal substitutes in cement manufacturing. The estimated emissions were determined using the CO2 emission factor for coal of 96.43 Mg CO2. The calculation reveals that the net emission of CO2 was reduced by about 25%, which was achieved by the co-combustion of 70% alternative fuels with a CO2 emission factor below 96.43 Mg CO2. In the case of fuel samples with a CO2 emission factor above 96.43 Mg CO2, the decline in emissions was slight, about 18%. In the analyzed case, an increase in the share of alternative fuels by each 10% resulted in a saving of coal mass by 19.43 Mg per hour, which generates savings of about 923 euros. In turn, the 10% reduction of coal burned means that about 0.56 TJ/h of thermal deficit must be supplemented with alternative fuel. This requires the burning of about 28–37 Mg of AF with the calorific value <20 MJ/kg and about 22–27 Mg of AF with the calorific value <20 MJ/kg within an hour. The total savings of approximately 1388 euros per hour were calculated for each 10% increase in alternative fuels. The cost reduction resulted from both the mass savings of the coal and the co-combustion of alternative fuels with the 30% biogenic fraction content. It has been proven that substituting coal with alternative fuels is one of the most prospective solutions, in terms of environmental protection and mitigating climate change. Co-combustion of AF reduces the consumption of high-emission fuels, thus enabling the fulfillment of the obligations stipulated by the Paris Agreement of 2015, i.e., the achieve- ment of the carbon neutrality targets to combat global climate change. At the same time, alternative fuels produced based on waste contribute to the implementation of the idea of a circular economy through using materials otherwise destined for landfills. Balancing off the cement plant’s environmental impact constitutes an urgent issue, particularly with the progressive maximization of energy consumption from waste-derived alternative fuels, and undoubtedly requires further detailed research. Future studies should focus on assessing the impact of the morphological composition of waste characterized by high heterogeneity on the amount of CO2 emissions coming from the combustion process.

Author Contributions: Conceptualization, K.W.-R. and A.S.; methodology, K.W.-R. and P.K.; valida- tion, K.W.-R., P.K., and A.S.; formal analysis, K.W.-R.; investigation, K.W.-R. and P.K.; writing— original draft preparation, K.W.-R.; writing—review and editing, K.W.-R. and A.S.; visualiza- tion, K.W.-R.; supervision, A.S. All authors have read and agreed to the published version of the manuscript. Energies 2021, 14, 1539 13 of 15

Funding: This research was funded by the Ministry of Science and Higher Education, Poland, grant number 11153010. Institutional Review Board Statement: The study was conducted according to the guidelines of the Declaration of Helsinki, and approved by the Institutional Review Board of Central Mining Institute (date of approval: 10 February 2021). Informed Consent Statement: Not applicable. Conflicts of Interest: The authors declare no conflict of interest.

References

1. Pardo, N.; Moya, J.A.; Mercier, A. Prospective on the energy efficiency and CO2 emissions in the EU cement industry. Energy 2011, 36, 3244–3254. [CrossRef] 2. Talaei, A.; Pier, D.; Iyer, A.V.; Ahiduzzaman, M.; Kumar, A. Assessment of long-term energy efficiency improvement and mitigation options for the cement industry. Energy 2019, 170, 1051–1066. [CrossRef] 3. Cloete, S.; Giuffrida, A.; Romano, M.C.; Zaabout, A. Economic assessment of the swing adsorption reactor cluster for CO2 capture from cement production. J. Clean. Prod. 2020, 275, 123024. [CrossRef] 4. Polish Cement Association. 2020. Available online: https://www.polskicement.pl/wyniki/ (accessed on 14 January 2021). 5. Statistical Review of World Energy, 69th ed; 2020. Available online: https://www.bp.com/content/dam/bp/business- sites/en/global/corporate/pdfs/energy-economics/statistical-review/bp-stats-review-2020-full-report.pdf (accessed on 14 January 2021). 6. Mokhtar, A.; Nasooti, M. A decision support tool for cement industry to select energy efficiency measures. Energy Strateg. Rev. 2020, 28, 100458. [CrossRef] 7. Habert, G. Assessing the environmental impact of conventional and ‘green’ cement production. In Eco-Efficient Construction and Building Materials; Elsevier: Amsterdam, The Netherlands, 2014. [CrossRef] 8. CEMBUREAU The European Cement Association. Cementing the European Green Deal, Reaching Climate Neutrality along the Cement and Concrete Value Chain by 2050. Available online: https://cembureau.eu/media/kuxd32gi/cembureau-2050 -roadmap_final-version_web.pdf (accessed on 29 July 2020). 9. Saidur, R.; Hossain, M.S.; Islam, M.R.; Fayaz, H.; Mohammed, H.A. A review on kiln system modeling. Renew. Sustain. Energy Rev. 2011, 15, 2487–2500. [CrossRef] 10. Gao, T.; Shen, L.; Shen, M.; Liu, L.; Chen, F. Analysis of material flow and consumption in cement production process. J. Clean. Prod. 2016, 112, 553–565. [CrossRef] 11. Kutery´nska,J.; Król, A. New types of low-carbon with reduced Portland clinker content as a result of ecological actions of cement industry towards sustainable development. J. Environ. Stud. 2016, 16, 403–419. 12. Navarrete, I.; Vargas, F.; Martinez, P.; Paul, A.; Lopez, M. Flue gas desulfurization (FGD) fly ash as a sustainable, safe alternative for cement-based materials. J. Clean. Prod. 2021, 283, 124646. [CrossRef] 13. Supino, S.; Malandrino, O.; Testa, M.; Sica, D. Sustainability in the EU cement industry: The Italian and German experiences. J. Clean. Prod. 2016, 112, 430–442. [CrossRef] 14. Chatziaras, N.; Psomopoulos, C.S.; Themelis, N.J. Use of waste derived fuels in cement industry: A review. Manag. Environ. Qual. Int. J. 2016, 27, 178–193. [CrossRef] 15. Kobize. Calorific Values (CO) and CO2 Emission Factors (EC) in 2016 for Reporting under the Emission Trading Scheme for 2019. Available online: https://www.kobize.pl/uploads/materialy/WO_i_WE_do_monitorowania-ETS-2019.pdf (accessed on 29 July 2020). 16. Wzorek, M.; Król, A. Assessment of the quality of fuels from waste used in coal co-firing processes. Sci. Work. Inst. Ceram. Build. Mater. 2012, 5, 444–465. 17. Regulation of the Minister of Climate of 2 January 2020 on the Catalogue of Wastes. (Journal of Laws of 2020 item 10). 2020. Available online: https://www.gov.pl/attachment/f4905905-e985-4344-a79e-71e51163afac (accessed on 10 March 2021). 18. European Standard. Solid Recovered Fuels—Terminology, Definitions and Descriptions; EN 15357:2011; CEN: Brussels, Belgium, 2011. 19. Manninen, H. Co-combustion of refuse derived and packaging-derived fuels (RDF and PDF) with conventional fuels. Waste Manag. Res. 1997, 15, 137–147. [CrossRef] 20. Martignon, G.P. Trends in the Use of Solid Recovered Fuels; IEA Bioenergy: Paris, France, 2020. Available online: https://www. ieabioenergy.com/wp-content/uploads/2020/05/Trends-in-use-of-solid-recovered-fuels-Main-Report-Task36.pdf (accessed on 3 March 2021). 21. Kang, S.; Kim, S.; Lee, J.; Jeon, Y.; Kim, K.H.; Jeon, E. Study on applying biomass fraction for greenhouse gases emission estimation of a sewage sludge incinerator in Korea: A case study. Sustainability 2017, 9, 557. [CrossRef] 22. Wojtacha-Rychter, K.; Smolinski, A. The CO2, CO and H2 emission profile from thermal oxidation of Polish . Materials 2020, 13, 848. [CrossRef][PubMed] Energies 2021, 14, 1539 14 of 15

23. Koteras, A.; Checko, J.; Urych, T.; Magdziarczyk, M.; Smolinski, A. An Assessment of the Formations and Structures Suitable for Safe CO2 Geological Storage in the Upper Silesia Coal Basin in Poland in the Context of the Regulation Relating to the CCS. Energies 2020, 13, 195. [CrossRef] 24. Che´cko,J.; Urych, T.; Magdziarczyk, M.; Smoli´nski,A. Research on the processes of injecting CO2 into coal seams with CH4 recovery using horizontal wells. Energies 2020, 13, 416. [CrossRef] 25. Zhou, W.; Jiang, D.; Chen, D.; Griffy-Brown, C.; Jin, Y.; Zhu, B. Capturing CO2 from cement plants: A priority for reducing CO2 emissions in China. Energy 2016, 106, 464–474. [CrossRef] 26. Chatterjee, A.; Sui, T. Alternative fuels–effects on clinker process and properties. Cem. Concr. Res. 2019, 123, 105777. [CrossRef] 27. Serrano-González, K.; Reyes-Valdez, A.; Chowaniec, O. Impact of the use of alternative fuels on clinker reactivity. Mater. Construcc. 2017, 67, 120. [CrossRef] 28. Strigáˇc,J. Effect of Selected Alternative Fuels and Raw Materials on the Quality. Sel. Sci. Pap. J. Civ. Eng. 2015, 10, 81–92. [CrossRef] 29. European Cement Association. 2019 Activity Report. 2019. Available online: http://www.cembureau.eu/media/clkdda45/ activity-report-2019.pdf (accessed on 1 March 2021). 30. Gonçalves, M.C.; Margarido, F. Materials for Construction and Civil Engineering, 2015th ed.; Springer International Publishing: Cham, Switzerland, 2015. [CrossRef] 31. Kurdowski, W. Cement and Concrete Chemistry; Springer: Dordrecht, The Netherlands, 2014. [CrossRef] 32. Stafford, F.N.; Dias, A.C.; Arroja, L.; Labrincha, J.A.; Hotza, D. Life cycle assessment of the production of : A Southern Europe case study. J. Clean. Prod. 2016, 126, 159–165. [CrossRef] 33. Ł ˛aczny, M.J.; Iwaszenko, S.; Smolinski, A. Process kinetics of the carbonation of fly ashes and their utilization as cement and concrete admixtures: A research study. Materials 2021, 14, 253. [CrossRef][PubMed] 34. Rahman, A.; Rasul, M.G.; Khan, M.M.K.; Sharma, S. Impact of alternative fuels on the cement manufacturing plant performance: An overview. Procedia Eng. 2013, 56, 393–400. [CrossRef] 35. 2006 IPCC Guidelines for National Greenhouse Gas Inventories, Volume 2, Energy, Stationary Combustion. 2006. Available online: https://www.ipcc-nggip.iges.or.jp/public/2006gl/pdf/2_Volume2/V2_2_Ch2_Stationary_Combustion.pdf (accessed on 1 March 2021). 36. Pamungkas, B.C.; Hadi, H. Potential of biomass utilization in rotary kiln of processing plant. IOP Conf. Ser. Mater. Sci. Eng. 2019, 588, 12006. [CrossRef] 37. Johnke, B. Background Papers. IPCC Expert Meetings on Good Practice Guidance and Uncertainty Management in National Greenhouse Gas Inventories; Emission from Waste Incineration; Intergovernmental Panel on Climate Change (IPCC): Geneva, Switzerland, 2020; pp. 455–468. Available online: https://www.ipcc-nggip.iges.or.jp/public/gp/bgp/5_3_Waste_Incineration.pdf (accessed on 14 December 2020). 38. Mikulcic, H.; Vujanovic, M.; Markovska, N.; Filkoski, R.; Ban, M.; Duic, N. CO2 emission reduction in the cement industry. Chem. Eng. Trans. 2013, 35, 703–708. [CrossRef] 39. European Energy Exchange. EUA Primary Market Auction Report 2020. Emission Spot Primary Market Auction Report 2020. 2020. Available online: https://www.eex.com/en/market-data/environmental-markets/eua-primary-auction-spot-download (accessed on 30 December 2020). 40. Schwarzböck, T.; Aschenbrenner, P.; Spacek, S.; Szidat, S.; Rechberger, H.; Fellner, J. An alternative method to determine the share of fossil carbon in solid refuse-derived fuels—Validation and comparison with three standardized methods. Fuel 2018, 220, 916–930. [CrossRef] 41. Gerassimidou, S.; Velis, C.A.; Williams, P.T.; Komilis, D. Characterisation and composition identification of waste-derived fuels obtained from municipal solid waste using thermogravimetry: A review. Waste Manag. Res. 2020, 38, 942–965. [CrossRef] 42. Samolada, M.C.; Zabaniotou, A.A. Energetic valorization of SRF in dedicated plants and cement kilns and guidelines for application in Greece and Cyprus. Resour. Conserv. Recycl. 2014, 83, 34–43. [CrossRef] 43. Rezaei, H.; Yazdan Panah, F.; Lim, C.J.; Sokhansanj, S. Pelletization of Refuse-Derived Fuel with Varying Compositions of Plastic, Paper, Organic and Wood. Sustainability 2020, 12, 4645. [CrossRef] 44. Zygadło,˙ M.; Purgał, P. The benefits of partial substitution of fossil fuel with alternative fuel in cement plant. Case study. Environ. Prot. Eng. 2020, 46.[CrossRef] 45. Iacovidou, E.; Hahladakis, J.; Deans, I.; Velis, C.; Purnell, P. Technical properties of biomass and solid recovered fuel (SRF) co-fired with coal: Impact on multi-dimensional resource recovery value. Waste Manag. 2018, 73, 535–545. [CrossRef] 46. U.S. Energy Information Administration (EIA). Coal Prices and Outlook. 2019. Available online: https://www.eia.gov/ energyexplained/coal/prices-and-outlook.php (accessed on 7 July 2020). 47. Sroda,´ B. Climate Neutrality and the Prospects for the Use of Concrete and Cement in Construction. Polish Cement Association. Available online: https://kongresdrogowy.pl/files/upload/OST2020_BSroda.pdf (accessed on 1 March 2021). 48. Kucharski, P.; Białecka, B. Poultry manure as a substrate for agriculture and the chemical industry. Int. Multidiscip. Sci. Geo Conf. SGEM 2019, 19, 611–618. [CrossRef] 49. Pröll, T.; Zerobin, F. Biomass-based negative emission technology options with combined heat and power generation. Mitig. Adapt. Strateg. Glob. Chang. 2019, 24, 1307–1324. [CrossRef] Energies 2021, 14, 1539 15 of 15

50. IPCC. Agriculture, Forestry and Other Land Use. Intergovernmental Panel on Climate Change, IPCC Guidelines for National Greenhouse Gas Inventories. 2006. Available online: http://www.ipcc-nggip.iges.or.jp/public/2006gl/vol4.html (accessed on 3 March 2021). 51. Thakur, A.; Canter, C.E.; Kumar, A. Life-cycle energy and emission analysis of power generation from forest biomass. Appl. Energy 2014, 128, 246–253. [CrossRef] 52. Petersen Raymer, A.K. A comparison of avoided greenhouse gas emissions when using different kinds of wood energy. Biomass Bioenergy 2006, 30, 605–617. [CrossRef] 53. Sedjo, R.A. Comparative Life Cycle Assessments: Carbon Neutrality and Wood Biomass Energy; Discussion Papers; Resources for the Future: Washington, DC, USA, 2013; pp. 11–13. [CrossRef] 54. Börjesson, P.; Gustavsson, L. Greenhouse gas balances in building construction: Wood versus concrete from life-cycle and forest land-use perspectives. Energy Policy 2000, 28, 575–588. [CrossRef] 55. Johnson, E. Goodbye to carbon neutral: Getting biomass footprints right. Environ. Impact Assess. Rev. 2009, 29, 165–168. [CrossRef] 56. Sanjuán, M.Á.; Andrade, C.; Mora, P.; Zaragoza, A. Carbon dioxide uptake by cement-based materials: A Spanish case study. Appl. Sci. 2020, 10, 339. [CrossRef]