Syngas Composition: Gasification of Wood Pellet with Water Steam

energies

Article Syngas Composition: Gasiﬁcation of Wood Pellet with Water Steam through a Reactor with Continuous Biomass Feed System

Jerzy Chojnacki 1,* , Jan Najser 2, Krzysztof Rokosz 1 , Vaclav Peer 2, Jan Kielar 2 and Bogusława Berner 1

1 Faculty of Mechanical Engineering, Koszalin University of Technology, Raclawicka Str.15-17, 75-620 Koszalin, Poland; [email protected] (K.R.); [email protected] (B.B.) 2 ENET Centre, VSB—Technical University of Ostrava, 17. Listopadu 2172/15, 708 00 Ostrava, Czech Republic; [email protected] (J.N.); [email protected] (V.P.); [email protected] (J.K.) * Correspondence: [email protected]; Tel.: +48-94-3478-359

Received: 15 July 2020; Accepted: 22 August 2020; Published: 25 August 2020

Abstract: Investigations were performed in relation to the thermal gasification of wood granulate using steam in an allothermal reactor with electric heaters. They studied the impact of the temperature inside the reactor and the steam flow rate on the percentage shares of H2, CH4, CO, and CO2 in synthesis gas and on the calorific value of syngas. The tests were conducted at temperatures inside the reactor equal to 750, 800, and 850 C and with a steam flow rate equal to 10.0, 15.0, and 20.0 kg h 1. ◦ · − The intensity of gasified biomass was 20 kg h 1. A significant impact of the temperature on the · − percentages of all the components of synthesis gas and a significant impact of the steam flow rate on the content of hydrogen and carbon dioxide in syngas were found. The highest percentage of hydrogen obtained was 43.3%. The calorific value of the gas depended significantly on the temperature inside the reactor and the correlation between the temperature and the steam flow rate. Its maximum value was 13.3 MJ m 3 at 800 C. This paper also includes an assessment of the mutual correlations of the · − ◦ percentage shares of the individual synthesis gas components.

Keywords: biomass; steam gasiﬁcation; allothermal reactor

1. Introduction Biomass can be used as a biorenewable resource of many advanced materials [1], but it is also a very important fuel recognized as a renewable energy source [2]. The direct combustion of some plant products in boilers may release many substances that are harmful to the environment [3]. The gasification of biomass at high temperatures enables the purification of the resulting gases before combustion and makes it possible to control the emission of pollutants. Thermal gasification can help destroy waste (e.g., municipal waste) and convert the energy contained in it into heat or electricity [4]. The simple biomass gasification in reactors through partial combustion in a limited air stream results in the production of a gas with a lower heat value (LHV), usually below 6 MJ Nm 3 [5,6]. · − Thermal gasification can be modified by introducing steam or oxygen instead of air into the gasifier, thus changing the composition of syngas produced [6–13]. In order to obtain the highest syngas energy value, attempts have been made to obtain the highest possible hydrogen and methane content and to minimize the share of carbon dioxide [12,14]. The high hydrogen content is achieved in the process of biomass gasification with the steam or thermal gasification of moist biomass [15–18]. The most popular raw materials used for the thermal gasification of biomass with the participation of water vapor is wood in various forms as sawdust, dust, chips, and granulates [9,19,20]. Apart from

Energies 2020, 13, 4376; doi:10.3390/en13174376 www.mdpi.com/journal/energies Energies 2020, 13, 4376 2 of 14 wood, typical cultivated energy crops [21] and waste biomass such as straw and hay [22,23], sewage sludge and manure [24–26] as well as biocarbon from previous biomass gasification may undergo steam gasification [12,27]. The raw materials for gasification may also include waste from the agri-food industry (e.g., oil production pomace [28], grape pomace [7], grain that was used in distilleries and in breweries [10,20,29], coffee hulls [30] and hazelnut shells [6]). Water steam gasification can be used not only in relation to biomass, but also in the process of the thermal gasification of hard coal, peat, and municipal waste as well as plastics [31–35]. Research is being carried out on the use of CO2 obtained from the combustion of syngas to increase the volume of syngas generated during the thermal gasification of municipal waste, particularly where increasing the CO2/steam ratio can facilitate the production of both CO and H2 in the resulting gas [33]. Research is also being conducted on the co-gasification of hard coal with biomass where a synergy effect was observed. The volume of hydrogen produced is increasing in relation to the gasification tests of the biomass and coal itself [31]. As a result of high-temperature biomass gasification including water steam gasification, the resulting gas is contaminated, mainly with dust and tar. In order to be introduced into turbines and combustion engines, especially into fuel cells, it must be purified [23,26]. The filter sets composed from the cyclones and porous materials are used to treat the mechanical impurities from fine particles in syngas. Very high gasification temperatures [36] and catalysts introduced into the system can also be used to remove chemical impurities [37,38]. Calcium compounds such as dolomite are most commonly used as CO2 and tar sorbents in the gasification process [26]. The share of water vapor in the thermal gasification of biomass can take place in various types of gasifiers. These can be autothermal gasifiers, where biomass is heated by means of heat obtained from partial combustion, and allothermal gasifiers, where heat is supplied from external sources [10,34,35]. Biomass was gasified with water steam in fixed-bed gasifiers and in reactors with a continuous flow of biomass and produced gas [21,23,31,38]. Biomass steam gasification was tested in a reactor with free biomass fall and lower syngas take-off [27] and in mono or dual fluidized bed reactors [8,9,24,29,33,39–41]. In autothermal fluidized bed gasifiers, a gasifying medium is used to maintain the particles in the suspension of the gas to be gasified. This is usually air or oxygen. In the case of the allothermal gasifier where steam is the only gasifying medium, steam is also used to support the fluidization process and to lift the particles [11,35]. Since the purpose of thermal gasification with water steam is to obtain synthesis gas with the highest possible calorific value, the aim is to convert carbon dioxide produced during gasification into carbon monoxide and methane and to use it to enrich syngas with hydrogen. Exothermic and endothermic reactions occurring during this process are described by chemical equations cited by the authors in [11,21,25,35,42]. The most important chemical reaction equations are the following: Char oxidation: C + O CO (1) 2 → 2 Boudouard reaction: CO + C 2CO (2) 2 ↔ Water–gas shift reaction: CO + H O CO + H (3) 2 ↔ 2 2 Water–gas reaction: C + H O CO + H (4) 2 ↔ 2 Thermal cracking: CnHm C + CxHy + H (5) → 2 Based on the thermodynamic equilibrium equations, mass and energy balances, and dedicated computer software, attempts have been made to model the gasification processes, while taking into account the individual stages of the process [40,42–44]. The results of the experimental and model investigations that have been conducted to date indicate that there are optimal ranges for the Energies 2020, 13, x FOR PEER REVIEW 3 of 14 Energies 2020, 13, 4376 3 of 14 investigations that have been conducted to date indicate that there are optimal ranges for the steam contentsteam content in the ingasifying the gasifying medium. medium. This was This found, was found, among among others, others, during during gasification gasification with with an air–steaman air–steam mixture mixture [7]. [ 7The]. The results results demonstrated demonstrated that that the the composition composition of of synthesis synthesis gas gas produced during water steam gasification gasification an andd its calorific calorific value as well as th thee relations between the shares of H2 and CO contained therein, may depend on the gasification temperature and the steam to biomass H2 and CO contained therein, may depend on the gasification temperature and the steam to biomass ratio [11,13,18,40]. [11,13,18,40]. Many experiments concerning biom biomassass gasification gasification with steam we werere carried out in autothermal reactors with the use of air or oxygen mostly in smallsmall laboratory gasifiers.gasifiers. The novelty of this work is that thethe researchresearch waswas carried carried out out in in an an installation installation with with a large a large reactor reactor with with a continuous a continuous biomass biomass feed feedsystem system to obtain to obtain pure pure syngas syngas with with a high a high concentration concentration of methane of methane and hydrogen.and hydrogen. The aim of the research was to determine the influenceinfluence of temperature in the allothermal flow flow reactor and thethe influenceinfluence ofof thethe steam steam flow flow rate rate to to the the reactor, reactor, to to the the synthesis synthesis gas gas composition composition and and its itslower lower heat heat value. value. Steam Steam together together with thewith heat the generated heat generated in the reactorin the heatingreactor setsheating were sets the gasifyingwere the gasifying factors. An analysis of the percentage shares of the following gases was planned: H2, CH4, factors. An analysis of the percentage shares of the following gases was planned: H2, CH4, CO, CmHn CO, CmHn as well as CO2 and O2 in the expected synthesis gas composition. as well as CO2 and O2 in the expected synthesis gas composition.

2. Materials Materials and Methods

2.1. Gasification Gasification Installation The research was carried out on an installation for thermal biomass gasificationgasification located in the Energy Research Center of the VŠB-Technical UniversityUniversity of Ostrava, which producesproduces syngas used to drive power generators. The installation consisted of an electrically heated reactor with a continuous supply of biomass and steam, a set of devices for cleaning and cooling synthesis gas, and a gas composition analyzer. A view of the gasificationgasification reactor isis shownshown inin FigureFigure1 1..

Figure 1. Reactor view: 11—bottom—bottom of of the the reactor, reactor, 2—steam pipe, 3—ash collection, 4—vertical screw conveyor, 5—horizontal screw conveyor.conveyor.

The reactor was heated from below by means of a 20 kW oval electric heater and from above by means ofof ﬁve five bar bar heaters heaters with awith total a power total ofpowe 35 kW.r of Thermocouples 35 kW. Thermocouples for temperature for measurements temperature weremeasurements installed inwere the lowerinstalled and in upper the lower parts ofand the up reactorper parts to allow of the temperature reactor to adjustmentsallow temperature inside adjustmentsthe reactor. Duringinside the the reactor. tests, the During temperature the tests, was the recorded temperature in the was upper recorded part of in the the reactor, upper directly part of

Energies 2020, 13, 4376 4 of 14 Energies 2020, 13, x FOR PEER REVIEW 4 of 14 theover reactor, the bed. directly The material over the subjected bed. The to gasificationmaterial subjected as the biomass to gasification was wood as the pellets, biomass fed by was means wood of pellets,a biomass fed feeder,by means with of flowa biomass scales f installedeeder, with to controlflow scales the rateinstalled of the to biomass control the feed. rate From of the the biomass feeder, feed.the pellets From werethe feeder, fed into the the pellets reactor were from fed below, into th ontoe reactor a moving from grate,below, using onto horizontala moving andgrate, vertical using horizontalscrew conveyors. and vertical After screw the biomass conveyors. was incinerated, After the biomass the ash was fell fromincinerated, the grate the to theash bottomfell from of the gratereactor, to fromthe bottom which itof was the removed reactor, byfrom means which of ait screw was removed conveyor by to ameans closed of metal a screw container. conveyor The tankto a wasclosed emptied metal container. at the end The of the tank experiment. was emptied The at design the end of of the the reactor experiment. prevented The anydesign uncontrolled of the reactor air preventedfrom entering any ituncontrolled from the outside. air from entering it from the outside. The steam was produced by means of an electric generator. The The rate rate of of steam flow flow into the generator waswas adjustedadjusted by by valves valves and and by by means means of a of flow a flow meter meter mounted mounted on a pipe on witha pipe water with flowing water flowinginto the steaminto the generator. steam generator. The temperature The temperature of the water of the vapor water supplied vapor fromsupplied the generator from the togenerator the reactor to wasthe reactor 650 ◦C. was A diagram 650 °C. ofA thediagram complete of the biomass complete thermal biomass gasification thermal plant gasification including plant the equipmentincluding the for equipmentgas treatment for andgas analysistreatment is and shown analysis in Figure is shown2. in Figure 2.

Figure 2. DiagramDiagram of of the biomass gasiﬁcationgasification plant: 11—pellet—pellet dispenser, 2—reactor, 3—cyclone separator, 4—dolomite reactor, 5—water cooler, 6—high temperature filter, ﬁlter, 7—cooler, 8—syngas analyzer, A—steam, B—gas, C—ash, D—dust, E—used dolomite,dolomite, FF—water,—water, GG—dust,—dust, HH—ice—ice water.water.

The syngas produced in the installation was designed to drive a power generator driven by a combustion engine.engine. InIn order order to to meet meet the the requirements requirements concerning concerning the puritythe puri ofty the of gas the used gas toused power to powerthe engine, the engine, the syngas the wassyngas cleaned was bycleaned means by of ameans set of of multiple a set of devices multiple [45 ].devices Dust was [45]. removed Dust was by removedmeans of by a cyclone means of separator a cyclone (marked separator with (marked the number with the 3) andnumber with 3) a dustand with filter a (No. dust 6).filter A reactor(no. 6). withA reactor a dolomite with a catalystdolomite was catalyst used towas eliminate used to tar eliminate from the tar gas. from The the gas gas. temperature The gas temperature was reduced was by reducedpassing itby through passing a it water through cooler a water fed with cooler running fed with water running from a water from system a water and ice system water and coolers. ice waterThe installation coolers. The was designedinstallation and was constructed designed in an cooperationd constructed with thein cooperation Czech company with ATEKO the Czech a.s. company ATEKO a.s. 2.2. Materials 2.2. MaterialsA constant flow rate of the wood pellet into the generator was accepted for the purpose of this study, which was 20 kg h 1. The laboratory-determined physical parameters of the pellets are shown A constant flow rate· − of the wood pellet into the generator was accepted for the purpose of this study,in Table which1. The was elemental 20 kg∙h composition−1. The laboratory-determined of the granulate is physical shown in parameters Table2. of the pellets are shown The flow rate of steam into the generator was adjusted to 10.0, 15.0, and 20.0 kg h 1. The ratio in Table 1. The elemental composition of the granulate is shown in Table 2. · − of theThe steam flow rate rate toof thesteam rate into of thethe biomassgenerator of was pellets adjusted introduced to 10.0, into 15.0, the and S/ 20.0B reactor kg∙h−1 was. The 0.5, ratio 0.75, of theand steam 1.0, respectively. rate to the rate of the biomass of pellets introduced into the S/B reactor was 0.5, 0.75, and 1.0, respectively.

Energies 2020, 13, 4376 5 of 14

Table 1. Physical parameters of the pellet.

Parameter Size Symbol Diameter 6 mm Length 10–30 mm Bulk density 650 kg m 3 · − Humidity 8.67 % hm. Caloriﬁc value 17.5 MJ kg 1 · − Ash content <0.6 % Attrition 2 %

Table 2. Elemental composition of the granulate.

Ingredients Contents % C 47.43 H 6.10 N 0.04 O 40.00 S 0.05 Cl 0.013 Ash 0.39

2.3. Methods A Portable Syngas Analyzer Gas 3100 was used to measure the percentage composition of the generator gas. The analyzer was connected to a pipe with cooled and purified gas coming out of the installation. The gas samples were collected by means of a ball valve probe equipped with a heated fiberglass filter trap, where solids and some tar particles were captured. Then, the gas flowed through vessels filled with isopropanol, where tar residues were removed from the gas. The gas then passed through three covered dishes placed in a freezer, where all the remaining organic substances and moisture were precipitated. With the help of the analyzer, the contents of CO, CO2, CH4,H2,O2, and CnHm in the synthesis gas were recorded continuously. The tests of the gas composition were performed with three temperatures set inside the reactor at 750, 800, and 850 ◦C. All parameters were measured continuously during the experiment and recorded by a computer. The test measurements were made after the set temperature inside the reactor had been reached and stabilized and after the steam flow rate and gas discharge pressure had been reached. The data were recorded once every minute for the measurement period of 10 min. The research was carried out on at installation for thermal biomass gasification located in the Energy Research Center of the VŠB—Technical University of Ostrava, which produces syngas used to drive power generators.

3. Results and Discussion The results of all the measurements of the concentrations of the gases tested, with each temperature and with each rate of steam flow, showed hydrogen, methane, hydrocarbon, carbon dioxide, and carbon monoxide contents and no free oxygen O2 content was found. The presence of CnHm hydrocarbons in syngas was negligible, never exceeding 0.8%. At a temperature of 850 ◦C, the content of this gas was equal to “0” for all the vapor flow rates and did not exceed 0.2% at 750 ◦C; hence, a decision was made to omit its content as a separate gas for further analyses and to add the CnHm concentrations determined in the syngas to the CH4 concentration. The averaged measurement results for the determined values of the temperature in the reactor and the steam flow rates are presented in Table3. The results of the measurements of the percentage share of hydrogen, methane, carbon dioxide, and carbon monoxide in synthesis gas underwent a two-factor analysis of variance in order to determine the significance of the impact of the following: Energies 2020, 13, x FOR PEER REVIEW 6 of 14 Energies 2020, 13, 4376 6 of 14 the steam outflow rate in the reactor and the temperature inside the reactor on the changes in the concentration of these components in the gas obtained. the steam outflow rate in the reactor and the temperature inside the reactor on the changes in the concentration of theseTable components 3. Averaged in measurement the gas obtained. results with standard deviations.

Table 3. H2% CH4% CO2% CO% Steam Flow Averaged measurement results with standard deviations. Temp °C −1 Stand. Stand. Stand. Stand. Ratio kg∙h Cont.H 2%Cont. CH 4%Cont. CO2% Cont. CO% Temp Steam Flow Dev. Dev. Dev. Dev. 1 Stand. Stand. Stand. Stand. 750 ◦C Ratio10 kg h 44.56Cont. 0.24 Cont.13.44 0.13 Cont.22.34 0.21 Cont.19.66 0.33 · − Dev. Dev. Dev. Dev. 750 15 43.34 0.49 13.72 0.29 21.64 0.75 21.30 0.88 750 75020 10 42.60 44.56 0.42 0.24 13.4414.15 0.130.28 22.3422.88 0.210.74 19.6620.37 0.33 0.51 750 15 43.34 0.49 13.72 0.29 21.64 0.75 21.30 0.88 800 10 38.30 5.10 15.56 1.54 23.87 3.74 22.27 7.55 750 20 42.60 0.42 14.15 0.28 22.88 0.74 20.37 0.51 800 80015 10 35.92 38.30 1.79 5.10 15.5616.90 1.540.58 23.8722.78 3.740.21 22.2724.40 7.55 1.29 800 80020 15 33.87 35.92 0.78 1.79 16.9017.08 0.580.39 22.7823.69 0.210.73 24.4025.37 1.29 1.19 850 80010 20 36.36 33.87 2.17 0.78 17.0812.34 0.391.52 23.6929.06 0.732.50 25.3722.24 1.19 3.17 850 85015 10 35.34 36.36 0.45 2.17 12.3411.02 1.520.47 29.0631.40 2.500.86 22.2422.24 3.17 0.85 850 15 35.34 0.45 11.02 0.47 31.40 0.86 22.24 0.85 850 20 35.58 0.27 10.99 0.16 34.00 0.42 19.43 0.44 850 20 35.58 0.27 10.99 0.16 34.00 0.42 19.43 0.44

3.1. Impact of the Steam Flow Rate on the Concentration of Synthesis Gas Components 3.1. Impact of the Steam Flow Rate on the Concentration of Synthesis Gas Components The impact of the steam flow rate on the concentrations of synthesis gas components is shown The impact of the steam ﬂow rate on the concentrations of synthesis gas components is shown in in Figure 3, which presents the average percentage shares of synthesis gas components calculated on Figure3, which presents the average percentage shares of synthesis gas components calculated on the the basis of the values obtained for all tested temperatures. basis of the values obtained for all tested temperatures.

100%

90% 21.4 22.6 21.7 80% 70% 25.1 25.3 26.9 60% 50% 14.1 14.2 14.4 40%

Gas content 30%

20% 39.5 37.9 37.0 10% 0% 10.0 15.0 20.0 Steam flow rate [kg∙h-1] H2 CH4 CO2 CO

Figure 3. Impact of the rate of steam outflow on the composition of synthesis gas (the least significant Figure 3. Impact of the rate of steam outflow on the composition of synthesis gas (the least significant difference at the significance level p < 0.05, for: H2 = 1.0%, CH4 = 0.4%, CO2 = 0.8%, CO = 1.5%). difference at the significance level p < 0.05, for: H2 = 1.0%, CH4 = 0.4%, CO2 = 0.8%, CO = 1.5%). The Figure3 shows the calculated values of the least significant di fferences (LSD) for each of these gases.The These Figure values 3 shows make the it possiblecalculated to values find the of value the least of the significant steam flow differences rate at which (LSD) a for significant each of dithesefference gases. in theThese gas values composition make occurred.it possible to find the value of the steam flow rate at which a significantNo significance difference ofin thethe impactgas composition of the steam occurred. flow rate on the percentage of CO and CH4 in the synthesisNo significance gas was found. of the However, impact theof impactthe stea ofm theflow steam rate flow on the rate percentage on the CO2 ofand CO H 2andconcentrations CH4 in the wassynthesis found gas to bewas significant. found. However, An increase the in theimpact steam of flowthe ratesteam in theflow reactor rate causedon the anCO increase2 and H in2 carbonconcentrations dioxide was and found a decrease to be in significant. hydrogen An content. increase The in optimum the steam hydrogen flow rate content, in the reactor an average caused of 39.5%,an increase was observedin carbon with dioxide the steamand a flowdecrease rate ofin 10hydrogen kg h 1, whichcontent. corresponded The optimum to hydrogen the S/B ratio content, of 0.5. · − Similaran average results of 39.5%, were presented was observed in [25 with,31]. the In other steam studies flow rate on theof 10 thermal kg∙h−1, gasification which corresponded of biomass to with the

Energies 2020, 13, x FOR PEER REVIEW 7 of 14 Energies 2020, 13, 4376 7 of 14 S/B ratio of 0.5. Similar results were presented in [25,31]. In other studies on the thermal gasification of biomass with steam, with or without air, the maximum share of hydrogen content in syngas was steam, with or without air, the maximum share of hydrogen content in syngas was obtained at higher obtained at higher S/B values [7,10,11,40]. S/B values [7,10,11,40].

3.2. Impact of the Temperature onon thethe ConcentrationConcentration ofof SynthesisSynthesis GasGas ComponentsComponents Based onon thethe valuesvalues obtained obtained for for all all tested tested steam steam flow flow ratios, ratios, the the average average percentage percentage shares shares of the of gasesthe gases included included in the in synthesis the synthesis gas were gas determined were deter formined particular for particular temperatures temperatures in order toin assess order the to significanceassess the significance of the impact of ofthe the impact temperature of the temper in the generatorature in the on generator the composition on the ofcomposition the gas. The of least the significantgas. The least differences significant were differences determined were for each determi of thesened syngasfor each ingredients of these syngas at the significance ingredients level at the of psignificance< 0.05. level of p < 0.05. Using the calculated values of the least significantsignificant didifferencesfferences to compare the changes in the contents of the the individual individual gases gases depending depending on on the the temperature temperature inside inside the thereactor, reactor, it can it canbe noted be noted that a significant decrease in hydrogen content in the synthesis gas occurred between 750 and 800 °C. The that a significant decrease in hydrogen content in the synthesis gas occurred between 750 and 800 ◦C. highest percentage share of H2 in the synthesis gas was 43.3% and it occurred at the lowest reactor The highest percentage share of H2 in the synthesis gas was 43.3% and it occurred at the lowest reactor temperature of 700 °C. The methane content of synthesis gas increased significantly between 750 and temperature of 700 ◦C. The methane content of synthesis gas increased significantly between 750 and 800 °C and then decreased between 800 and 850 °C. The carbon dioxide content increased 800 ◦C and then decreased between 800 and 850 ◦C. The carbon dioxide content increased significantly significantly between 800 and 850 °C. The carbon monoxide content increased significantly at 800 °C, between 800 and 850 ◦C. The carbon monoxide content increased significantly at 800 ◦C, and then and then returned to the previous level at 850 °C (Figure 4). returned to the previous level at 850 ◦C (Figure4).

100%

90% 20.4 24.0 21.3 80% 70% 22.3 23.4 60% 31.5 50% 14.0 17.2 40% 11.5

Gas content 30% 43.3 20% 35.4 35.7 10% 0% 750 800 850 Temperature in reator [oC] H2 CH4 CO2 CO

Figure 4. Impact of the temperature in the reactor on the composition of the generated gas (the least Figure 4. Impact of the temperature in the reactor on the composition of the generated gas (the least significant difference at a significance level p < 0.05 for H2 = 1.0%, CH4 = 0.4%, CO2 = 0.8%, CO = 1.5%). significant difference at a significance level p < 0.05 for H2 = 1.0%, CH4 = 0.4%, CO2 = 0.8%, CO = 1.5%). 3.3. Impact of Reactor Temperature and the Steam Flow Rate on the Syngas Heat Value 3.3. Impact of Reactor Temperature and the Steam Flow Rate on the Syngas Heat Value The results of the syngas calorific value determined with the GAS 3100 Syngas gas analyzer were also coveredThe results by aof two-factor the syngas variance calorific analysis value todeter calculatemined thewith significance the GAS 3100 of the Syngas impact gas of the analyzer steam flowwere rate also and covered the temperature by a two-factor inside variance the reactor analysis on the to syngas calculate energy the value. significance The analysis of the demonstratedimpact of the thesteam significance flow rate of and the the impact temperature of the temperature inside the and reactor the significance on the syngas of the energy impact value. of the The temperature analysis anddemonstrated steam flow the rate significance correlation of on the the impact syngas of calorific the temperature value. A diagramand the significance that shows the of the impact impact of the of temperaturethe temperature in the and reactor steam on flow the rate lower correlation heat value on of the synthesis syngas calorific gas is shown value. in A Figure diagram5. that shows the impactNo significance of the temperature was found inin thethe impactreactor of on the the steam lower flow heat rate value alone of on synthesis the changes gas in isthe shown syngas in heatFigure value. 5. The maximum lower heat value of the synthesis gas was obtained at 800 ◦C. A further increaseNo insignificance temperature was up found to 850 ◦inC the in the impact generator of th resultede steam inflow a decrease rate alone in the on heat the valuechanges of thein gasthe generated.syngas heat By value. analyzing The maximum the composition lower heat of syngas valueat of this the temperature,synthesis gas it was can obtained be concluded at 800 that °C. the A decreasefurther increase in the energy in temperature value was up influenced to 850 °C by in thethe increasegenerator in resulted the percentage in a decrease of CO2 inand the the heat decrease value inof thethe CO gas and generated. CH4 contents. By analyzing the composition of syngas at this temperature, it can be

Energies 2020, 13, x FOR PEER REVIEW 8 of 14 Energies 2020, 13, x FOR PEER REVIEW 8 of 14 concluded that the decrease in the energy value was influenced by the increase in the percentage of concluded that the decrease in the energy value was influenced by the increase in the percentage of CO2 and the decrease in the CO and CH4 contents. Energies 2020, 13, 4376 8 of 14 CO2 and the decrease in the CO and CH4 contents.

] 14.0 -3

] 14.0

-3 12.0 12.0 10.0 10.0 8.0 8.0 6.0 12.1 13.0 6.0 12.1 13.0 10.4 4.0 10.4 4.0 2.0 Lower Heat Value [MJ∙m Value Heat Lower 2.0 Lower Heat Value [MJ∙m Value Heat Lower 0.0 0.0 700 750 800 700Temperature 750 in reator [oC] 800 Temperature in reator [oC]

Figure 5. Impact of the temperature in the reactor on the syngas lower heat value. Figure 5. Impact of the temperature in the reactor on the syngas lower heat value. Figure 5. Impact of the temperature in the reactor on the syngas lower heat value. TheThe impactimpact ofof the the correlation correlation between between the the reactor reactor temperature temperature and and the the steam steam outflow outflow rate rate on theon The impact of the correlation between the reactor temperature and the steam outflow rate on syngasthe syngas heat heat value value is shown is shown in Figure in Figure6. The 6. The calorific calorific value value of synthesis of synthesis gas gas obtained obtained at the at the level level of the syngas heat value is shown in Figure 6. The calorific value of synthesis gas obtained at the level 13.3of 13.3 MJ mMJ∙3mat−3 theat the temperature temperature of 800 of 800C, and °C, theand steam the steam inflow inflow rate of rate 15.0 of and 15.0 20.0 and kg h20.01 was kg∙h typical−1 was of 13.3 MJ· −∙m−3 at the temperature of 800◦ °C, and the steam inflow rate of 15.0 and 20.0· − kg∙h−1 was fortypical the thermalfor the thermal gasification gasification of biomass of biomass with these with conditions these conditions [6,13]. [6,13]. typical for the thermal gasification of biomass with these conditions [6,13]. ]

-3 14.0 ]

-3 14.0 12.0 12.0 10.0 10.0 8.0 8.0 13.3 6.0 12.2 12.4 13.3 12.0 12.1 13.3 13.3 6.0 12.0 12.2 12.1 12.4 10.7 10.4 10.1 4.0 10.7 10.4 10.1 4.0 2.0

Lower Heat Value [MJ∙m Value Heat Lower 2.0

Lower Heat Value [MJ∙m Value Heat Lower 0.0 0.0 750 800 850 750Temperature 800 in generator [oC] 850 o Temperature 10in generator15 20 [ C] 10 15 20 1 Figure 6. Impact of temperature in the generator and the steam outflow rate (10; 15; 20 kg h− ) on the Figure 6. Impact of temperature in the generator and the steam outflow rate (10; 15; 20 kg· ∙h−1) on the syngas lower heat value. −1 Figuresyngas 6. lower Impact heat of value.temperature in the generator and the steam outflow rate (10; 15; 20 kg∙h ) on the 3.4. Correlationssyngas lowerbetween heat value. the Content of the Individual Syngas Components 3.4. Correlations between the Content of the Individual Syngas Components 3.4. CorrelationsThe basic componentsbetween the Content of gasified of the woodIndividual biomass Syngas and Components introduced water vapor such as O2,H2, and CThe were basic in the components reactor. The of amount gasified and wood thepercentage biomass and content introduced of the produced water vapor gases such that constituteas O2, H2, theand components TheC were basic in components ofthe the reactor. syngas of The obtainedgasi amountfied wood in theand biomass reactor the percentage result and introduced directly content from water of the the mass vapor produced flow such rate asgases of O steam2, Hthat2, andandconstitute biomass,C were the in the components the temperature reactor. ofThein the the amount syngas reactor, obtainedand and the the percentage chemicalin the reactor processes content result describedof directly the produced byfrom Equations the gases mass (1)–(5), thatflow constitutewhichrate of took steam the place componentsand during biomass, the of the gasification the temperature syngas in obtained the in reactor. the in reactor, the An reactor analysis and the result of chemical the directly mutual processes correlationsfrom the described mass between flow by ratetheEquations percentageof steam (1)–(5), and contents biomass, which oftook the individual placetemperature during gases thein was the gasifi carriedreactor,cation out,and in the takingthe reactor. chemical into An account processes analysis the describedof results the mutual of by all Equationsmeasurements.correlations (1)–(5), between Figures which the7 tookand percentage8 placeshow during the contents percentage the gasifi of changesindividualcation in of the carbon gases reactor. monoxidewas An carried analysis and out, carbon of thetaking dioxide mutual into correlationscontentsaccount inthe the betweenresults syngas of the withall percentagemeasurements. an increasing contents methane Figures of percentage7individual and 8 show content.gases the waspercentage carried changesout, taking of carbon into accountmonoxide the andresults carbon of all dioxide measurements. contents Figures in the 7sy andngas 8 withshow anthe increasing percentage methane changes percentageof carbon monoxidecontent. and carbon dioxide contents in the syngas with an increasing methane percentage content.

EnergiesEnergies 20202020,, 13,, x 4376 FOR PEER REVIEW 99 of of 14 14 Energies 2020, 13, x FOR PEER REVIEW 9 of 14 38 38 36 36 34 34 32 32 30 30 28 28 26

CO [%] CO 26 24 CO [%] CO 24 22 22 20 20 18 18 16 16 14 14 8 9 10 11 12 13 14 15 16 17 18 19 8 9 10 11 12 13 14 15 16 17 18 19 CH4 [%] CH4 [%] Figure 7. Correlation between percentage content of CO and percentage content of CH4. Figure 7. Correlation between percentage content of CO and percentage content of CH . Figure 7. Correlation between percentage content of CO and percentage content of CH4. 36 36 34 34 32 32 30 30 28 28 26 26 CO2 [%] CO2 24 CO2 [%] CO2 24 22 22 20 20 18 18 16 16 8 9 10 11 12 13 14 15 16 17 18 19 8 9 10 11 12 13CH4 [%] 14 15 16 17 18 19 CH4 [%] Figure 8. Correlation between percentage content of CO and percentage content of CH . Figure 8. Correlation between percentage content of CO2 and percentage content of CH44. Figure 8. Correlation between percentage content of CO2 and percentage content of CH4. The CO content increased with the growing CH4 content. This relationship is described in the The CO content increased with the growing CH4 content. This relationship is described in the following regression equation: followingThe CO regres contentsion equation:increased with the growing CH4 content. This relationship is described in the following regression equation: CO = 10.552 + 0.81718 CH4 (6) · CO = 10.552 + 0.81718 ∙ CH (6) with the calculated correlation coeffiCOcient = 10.552r = 0.56371 + 0.81718 at the significance ∙ CH level of p = 0.95. (6) with Inthe the calculated case of COcorrelation, the content coefficient of this r gas= 0.56371 decreased at the significantly significance aslevel the of CH p = content0.95. increased. with the calculated correlation2 coefficient r = 0.56371 at the significance level of p 4= 0.95. The regressionIn the case equationof CO2, the is determined content of this as follows: gas decreased significantly as the CH4 content increased. The regressionIn the case equation of CO2, the is determined content of thisas follows: gas decreased significantly as the CH4 content increased. The regression equation is determined as follows: CO2 = 46.859 1.518 CH4 (7) CO = 46.859 −− 1.518· ∙ CH (7) CO = 46.859 − 1.518 ∙ CH (7) with the correlation coe fficient r = −0.7606,0.7606, at at the the significance significance level level pp == 0.95.0.95. with the correlation coefficient r = −−0.7606, at the significance level p = 0.95. TheThe relation relation between the CO 22 andand CO CO content content is is shown in Figu Figurere 99.. TheThe followingfollowing regressionregression equationequationThe relationwas was determined: determined: between the CO2 and CO content is shown in Figure 9. The following regression equation was determined: CO2 = 37.385 0.5313 CO (8) CO = 37.385 −− 0.5313· ∙ CO (8) with the correlation coefficient r = 0.3859CO = at 37.385 the significance − 0.5313 ∙ COlevel of p = 0.95. (8) with the correlation coefficient r = −−0.3859 at the significance level of p = 0.95. with theAn attemptcorrelation to findcoeffi thecient relation r = −0.3859 between at the CH significance4 and H2 is shownlevel of in p Figure= 0.95. 10.

Energies 2020, 13, x FOR PEER REVIEW 10 of 14 Energies 2020, 13, 4376 10 of 14 Energies 2020, 13, x FOR PEER36 REVIEW 10 of 14

34 36

32 34

30 32

28 30

26 28 CO2 [%] CO2 24 26

CO2 [%] CO2 22 24

20 22

18 20

16 1814 16 18 20 22 24 26 28 30 32 34 36 38 CO [%] 16 14 16 18 20 22 24 26 28 30 32 34 36 38 Figure 9. Correlation between COthe [%] percentage of CO2 and CO. Figure 9. Correlation between the percentage of CO and CO. Figure 9. Correlation between the percentage of CO2 and CO. An attempt to find the relation between CH4 and H2 is shown in Figure 10.

An attempt to find19 the relation between CH4 and H2 is shown in Figure 10.

18 19 17 18 16 17 15 16 14 15 13 CH4 [%] CH4 14 12 13 CH4 [%] CH4 11 12 10 11 9 10 8 928 30 32 34 36 38 40 42 44 46

8 H2 [%] 28 30 32 34 36 38 40 42 44 46 Figure 10. Correlation between theH2 percentage [%] content of CH4 and H2. Figure 10. Correlation between the percentage content of CH4 and H2 . The following regression equation was determined: The followingFigure regression 10. Correlation equation between was determined: the percentage content of CH4 and H2. CH4 = 18.278 0.1145 H2 (9) The following regression equationCH was = 18.278determined: −− 0.1145 · ∙ H (9) with the correlation coefficient r = −0.21550.2155 at at the the significance significance level level of of pp == 0.95.0.95. − CH = 18.278 − 0.1145 ∙ H (9) Correlations between the carbon monoxide and carbon dioxide contents, depending on the with the correlation coefficient r = −0.2155 at the significance level of p = 0.95. proportion of the hydrogen share, are shown in Fi Figuresgures 11 and 12.12. The The relations relations can be described by by Correlations between the carbon monoxide and carbon dioxide contents, depending on the thethe following regression equations: proportion of the hydrogen share, are shown in Figures 11 and 12. The relations can be described by COCO == 42.02342.023 − 0.52700.5270 H ∙ H2 (10)(10) the following regression equations: − ·

with the correlation coefficient r = −0.68420.6842CO = at at42.023 the the significance significance − 0.5270 ∙ level H level of of pp == 0.95,0.95, (10) − with the correlation coefficient r = −0.6842COCO = at= 38.841 the38.841 significance − 0.34350.3435 H∙level H of p = 0.95, (11)(11) 2 − · 2 with the correlation coefficient r = −0.3239CO = at 38.841 the significance − 0.3435 ∙level H of p = 0.95. (11) with the correlation coefficient r = 0.3239 at the significance level of p = 0.95. The determined equations demonstrate− a decrease in the carbon monoxide and carbon dioxide with Thethe correlation determined coe equationsfficient r demonstrate= −0.3239 at the a decrease significance in the level carbon of p monoxide= 0.95. and carbon dioxide contents as the hydrogen content of the syngas increases. contentsThe asdetermined the hydrogen equations content demonstrate of the syngas a decrease increases. in the carbon monoxide and carbon dioxide contents as the hydrogen content of the syngas increases.

Energies 2020, 13, 4376 11 of 14

EnergiesStrong 2020, 13 relations,, x FOR PEER with REVIEW a correlation coefficient higher than 0.5, occurred between the CO and11 COof 142 Energiescontents 2020 in, 13 relation, x FOR PEER to the REVIEW CH4 content, and between the CO content in relation to the H2 content.11 of 14 38 38 36 36 34 34 32 32 30 30 28 28 26 26 CO [%] CO 24 CO [%] CO 24 22 22 20 20 18 18 16 16 14 1428 30 32 34 36 38 40 42 44 46 28 30 32 34 36 38 40 42 44 46 H2 [%] H2 [%] Figure 11. Correlation between percentage of CO and H2 contents. Figure 11. Correlation between percentage of CO and H contents. Figure 11. Correlation between percentage of CO and H2 contents. 36 36 34 34 32 32 30 30 28 28 26 26 CO2 [%] CO2 24 CO2 [%] CO2 24 22 22 20 20 18 18 16 1628 30 32 34 36 38 40 42 44 46 28 30 32 34 36 38 40 42 44 46 H2 [%] H2 [%] Figure 12. Correlation between percentage of CO and H contents. Figure 12. Correlation between percentage of CO2 and H22 contents. Figure 12. Correlation between percentage of CO2 and H2 contents. 4. Conclusions Strong relations, with a correlation coefficient higher than 0.5, occurred between the CO and Strong relations, with a correlation coefficient higher than 0.5, occurred between the CO and CO2 contentsThe main in components relation to ofthe the CH synthesis4 content, gas and obtained between as thethe resultCO content of the thermalin relation gasification to the H of2 CO2 contents in relation to the CH4 content, and between the CO content in relation to the H2 content.wood granulate with steam are represented by the following gases: CO, CO2, CH4, and H2. The value content.of the content of these gases in the gas generated was significantly influenced by the temperature in 4.the Conclusions gas generator. An increase in the temperature between 750 and 850 ◦C had a significant impact on 4.the Conclusions decrease of the H , CH , and CO content and on the increase of the CO content. The main components2 4 of the synthesis gas obtained as the result of the2 thermal gasification of TheA significant main components impact of of the the steam synthesis flow rategas onobtained the concentration as the result of of H the2 and thermal CO2 in gasification the synthesis of wood granulate with steam are represented by the following gases: CO, CO2, CH4, and H2. The value gas was found. An increase in the steam flow rate in the generator caused a decrease in the share of ofwood the contentgranulate of withthese steam gases arein therepresented gas generated by the was following significantly gases: influencedCO, CO2, CH by4 ,the and temperature H2. The value in hydrogen and an increase in the share of carbon dioxide in the syngas. theof the gas content generator. of these An increasegases in inthe the gas temperatur generatede was between significantly 750 and influenced 850 °C had by a thesignificant temperature impact in the gasThere generator. was a significant An increase impact in the of thetemperatur temperaturee between of the 750 gas generatorand 850 °C on had the a calorific significant value impact of the on the decrease of the H2, CH4, and CO content and on the increase of the CO2 content. onsyngas. the decrease The highest of the calorific H2, CH value4, and ofCO the content synthesis and gas on wasthe increase obtained of at the 800 CO◦C.2 content. A significant impact of the steam flow rate on the concentration of H2 and CO2 in the synthesis This study has documented the existence of strong correlations between the carbon monoxide gas wasA significant found. An impact increase of inthe the steam steam flow flow rate rate on in the the concentration generator caused of H 2a and decrease CO2 in in the the synthesis share of and carbon dioxide contents and methane content as well as between the carbon monoxide content hydrogengas was found. and an An increase increase in in the the share steam of carbonflow rate dioxide in the ingenerator the syngas. caused a decrease in the share of and hydrogen content. hydrogenThere and was an a significantincrease in impactthe share of ofthe carbon temperature dioxide of in the the gas syngas. generator on the calorific value of the syngas.There wasThe ahighest significant calorific impact value of ofthe the temperature synthesis gas of thewas gas obtained generator at 800 on °C. the calorific value of the syngas. The highest calorific value of the synthesis gas was obtained at 800 °C.

Energies 2020, 13, 4376 12 of 14

The research on the thermal gasification of wood granulate using steam, carried out in an electrically heated flow reactor, has confirmed the significance of the impact of the following factors: the flow rate of steam supplied to the reactor and the temperature inside the reactor on the percentage share of the components of the syngas produced such as H2, CH4, CO, and CO2. The research has demonstrated a possibility of adjusting the values of these factors while obtaining the required syngas composition and considering its maximum calorific value.

Author Contributions: Conceptualization, J.C. and J.N.; methodology, J.C., J.N., K.R. and V.P.; software, B.B.; validation, J.C., K.R. and J.K.; formal analysis, J.K. and K.R.; data curation, J.C. and V.P.; writing—original draft preparation, J.C., V.P. and J.N.; writing—review and editing, J.C., K.R., B.B. and J.K.; visualization, B.B.; supervision, J.N.; project administration, J.C.; funding acquisition, J.C. and J.K. All authors have read and agreed to the published version of the manuscript. Funding: The research was performed within the framework of a project of bilateral exchange of researchers between the Republic of Poland and the Czech Republic titled “Use of catalysts to reduce emissions from the combustion of waste biomass” (reference no: PPN/BIL/2018/1/00074) co-financed in Poland by the NAWA, National Agency of Academic Exchange and supported by the Ministry of Education, Youth, and Sports of the Czech Republic under OP RDE grant number CZ.02.1.01/0.0/0.0/16_019/0000753 “Research center for low-carbon energy technologies”. Acknowledgments: The authors would like to thank Associate Professor Tadeas Ochodek, Director of the Energy Research Center of VŠB-Technical University of Ostrava, for making the laboratory available for carrying out tests and providing assistance during their performance. Conflicts of Interest: The authors declare no conflict of interest.

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