energies
Article Thermal Efficiency of Oxyhydrogen Gas Burner
Roberto Moreno-Soriano 1,2, Froylan Soriano-Moranchel 1, Luis Armando Flores-Herrera 1, Juan Manuel Sandoval-Pineda 1,* and Rosa de Guadalupe González-Huerta 2,* 1 Instituto Politécnico Nacional, Sección de Estudios de Posgrado e Investigación, ESIME-U. Azc., Av. de las Granjas 682, Col. Santa Catarina, Ciudad de México CP 02250, Mexico; [email protected] (R.M.-S.); [email protected] (F.S.-M.); luis.a.fl[email protected] (L.A.F.-H.) 2 Instituto Politécnico Nacional, ESIQIE, Laboratorio de Electroquímica, UPALM, Ciudad de México CP 07738, Mexico * Correspondence: [email protected] (J.M.S.-P.); [email protected] (R.d.G.G.-H.)
Received: 21 September 2020; Accepted: 16 October 2020; Published: 21 October 2020
Abstract: One of the main methods used to generate thermal energy is the combustion process. Burners are used in both industrial and residential applications of the open combustion process. The use of fuels that reduce polluting gas emissions and costs in industrial and residential processes is currently a topic of significant interest. Hydrogen is considered an attractive fuel for application in combustion systems due to its high energy density, wide flammability range, and only produces water vapor as waste. Compared to research conducted regarding hydrocarbon combustion, studies on hydrogen burners have been limited. This paper presents the design and evaluation of an oxyhydrogen gas burner for the atmospheric combustion process. The gas is generated in situ with an alkaline 1 electrolyzer with a production rate of up to 3 sL min− . The thermal efficiency of a gas burner is defined as the percentage of the input thermal energy transferred to the desired load with respect to a given time interval. The experimental results show a thermal efficiency of 30% for a minimum flow 1 1 rate of 1.5 sL min− and 76% for a flow rate of 3.5 sL min− . These results relate to a 10 mm height between the burner surface and heated container.
Keywords: oxyhydrogen gas; oxyhydrogen gas burner; thermal efficiency; alkaline electrolyzer
1. Introduction New environmental regulations for the generation of thermal energy with stationary systems have motivated the development of burners that use clean fuel. Hydrogen is considered a clean fuel under the electric industry law of the Mexican regulations issued in 2014 [1]. Two methods for hydrogen usage prevail: first, as the feed to fuel cells for electricity generation or, second, through a combustion process to generate heat. Worldwide efforts have been made to commercialize the proton exchange membrane fuel cell (PEMFC) in recent years; however, the cost of PEMFC is still considerably higher than that of conventional combustion devices (burners and internal combustion engines). Therefore, in the short term, hydrogen as a fuel will be implemented using the existing infrastructure, rendering the necessary changes and adaptations simple and inexpensive. This will facilitate the implementation of rules and regulations of hydrogen uses so that after a decade, the PEMFC could be used extensively [2,3]. In an atmospheric combustion process, hydrogen can be used alone or, in appropriate proportions, as a partial complementary substitute for natural gas (NG) or liquefied petroleum gas (LPG). When considering fuels with a high hydrogen content (>60%), factors such as the combustion velocity, temperature, and flashback or blow-off flame should be controlled with an appropriate burner design. Therefore, burners with a complex flow rate regime have been proposed, such as swirl burners, flat flame burners, micro-mix burners, and partial-premixed body burners. These devices operate with
Energies 2020, 13, 5526; doi:10.3390/en13205526 www.mdpi.com/journal/energies Energies 2020, 13, 5526 2 of 11 a highly optimized flow rate to achieve an efficient performance while ensuring minimal production of contaminants [2]. The lower calorific value of hydrogen is 122 kJ/g which is higher than that of other hydrocarbon fuels, such as gasoline with 45 kJ/g and NG with 42 kJ/g. Safety standards must be strictly adhered to when handling hydrogen, which has a safety factor equal to 1 compared with 0.8 and 0.53 for that of methane and gasoline, respectively. In contrast with methane and gasoline, hydrogen has a very low density, high diffusion coefficient, wider ignition limits, and higher ignition temperature. The full benefits of hydrogen as a clean, versatile, and efficient fuel will depend on the raw materials and processes used in its production [2–6]. Hydrogen can be produced from various renewable and non-renewable resources; currently, its production is based mainly on fossil fuel to the steam reforming process (96%). Electrolysis technology is used to produce the remaining 4%; however, energy is required to split the molecules. If electric current is produced by a renewable source (e.g., solar PV or a wind turbine), the clean hydrogen produced is known as green hydrogen; the objective is to eliminate fossil fuels from the water-splitting cycle. A water alkaline electrolyzer (WAE) utilizes a hydroxyl ions (OH−) solution, whereby the water molecule is separated into hydrogen and oxygen when direct current electrical energy is applied. This technology is prominent among others such as the proton exchange membrane electrolyzer (PEME) since it has the greatest maturity and many devices that offer the advantage of low cost and simplicity are commercially available [3,4]. In a WAE, hydrogen and oxygen can be produced separately if a membrane is used between the electrodes. Gases of 99.9% purity can be obtained in a water alkaline electrolyzer (WAE) with a basic purification system, which is suitable for combustion systems. The mixture of hydrogen and oxygen (2H2/O2) produced in stoichiometric proportions in the WAE without a membrane is known by various names, such as hydroxy gas, oxyhydrogen gas, and Brown gas; oxyhydrogen gas (OH2G) is used in this study. The first use of this gas was reported by Brown for welding processes. In recent years, OH2G has been used mainly as a supplement to fuels for internal combustion engines due to its excellent combustion properties. Most of the research studies conducted in the field of diesel and gasoline vehicle engines with OH2G dual-combustion resulted in lower fuel consumption, increased engine performance, and reduced emissions of polluting gases [5–7]. The H2OG should not be stored for safety reasons, its use is based on avoiding heavy and complex hydrogen storage systems, it should be produced in situ, using an alkaline electrolyzer, improving safety and eliminating storage systems. In addition, hydrogen can be used in some of the existing equipment and infrastructures designed for NG applications; several studies have shown that NG can be mixed with hydrogen as a fuel [8–13]. In the same way, OH2G can be used as a fuel in industrial and domestic applications, such as cutting and welding processes, domestic heating, or cooking. Uykur et al. [12] evaluated the addition of H2 (10–20%) and OH2G (10%) to methane. The results show that the addition of 10–20% H2 increases the flame combustion rate (SL) by 8–15%. Echeverri et al. [13] performed a numerical and experimental analysis of OH2G addition in laminar flames premixed with methane/air, obtaining a maximum increment of 14.8% in the rate of combustion with 25% OH2G in the gas mixture. Pan et al. [14] investigated the efficiency of a porous media micro combustor with numerical analysis. They considered OH G mixtures, the equivalence ratio ( ), and the 2 ∅ flow rate in the gas mixture. The results show enhanced efficiency for micro combustion with = 0.8 1 ∅ and a flow rate of 6 m s− . Tanneberger et al. [15] analyzed the efficiency of the combustion of OH2G under stoichiometric conditions by applying the concept of dilute (or wet) combustion with steam to reduce NOx and CO emissions. The results revealed: for temperatures above 826.85 ◦C, the combustion efficiency exceeds 95%, while at lower temperatures the efficiency decreases significantly [16]. This paper presents the design and evaluation of OH2G burners, where the OH2G is produced in situ using a WAE. The design analysis allows us to determine the optimal configuration (diameter, length, spacing, and number) of the flame ports in the burner, thus guaranteeing adequate combustion while simultaneously avoiding backlash or blow-off flame. Thermal evaluation of the flame generated allows us to quantify the efficiency of the OH2G burner; the relation between flame stability and gas flow rate produced in the WAE is obtained. The results provide an improved perspective on the advantages of using OH2G as the fuel gas, which can be used alone or in parallel with NG or LPG Energies 2020, 13, 5526 3 of 11 burners. Moreover, its implementation is simple and cheap, without the need for radical modifications to facilities.
2. Materials and Methods Burners used in domestic appliances are of the Bunsen type and are commonly referred to as atmospheric burners and consume commercial hydrocarbon gas (LPG or NG) as fuels. The materials used for these burners are carbon steel, stainless steel, copper, and brass, so its costs are accessible. Atmospheric burners need a portion of the air to be mixed with the gas before it reaches the burner ports; this is called primary air. The additional air required is taken from the atmosphere surrounding the flames and is termed secondary air. The primary air is the most important; if the volume is increased, a limit is established above which the flames either blow away from the ports or flashback into the burner, depending upon the gas rate used. Furthermore, the volume of the primary air decreases to a limit below which the combustion process is incomplete [16]. For OH2G burners, the operation principle and materials used for their manufacture are the same as the burners for NG and LPG. In this case, the stoichiometric amount of oxygen or primary air is already mixed with the fuel; therefore, the combustion process will depend only on the flow rate of oxyhydrogen gas (OH2G) produced in the WAE. The burner design is influenced by the type of fuel. Burner design analysis allows for the selection of a burner that delivers the most satisfactory performance, which includes an efficient combustion process, high heat transfer, and operational safety. One of the principal requisites of a well-designed burner is its capability to completely burn the gas supplied to it. The oxidizer-fuel rates can be used to adjust the design of the burner components (injector, throat, and head). Chemically, the complete combustion of oxyhydrogen is defined as (1):
2H + O 2H O (1) 2 2 → 2 The equivalence ratio ( ) given in Equation (2), is used to identify the quality and type of mixture ∅ (fuel/oxidizer) according to the flow rate characteristics of each gas: . ! . ! Ract mH2 mH2 ∅ = = . / . (2) R stoi mO2 act mO2 stoi where Ract represents the fuel/oxidizer ratio according to the gases supplied and Rstoi represents the . stoichiometric ratio to guarantee combustion of the gas mixture. mH is the mass flow rate of hydrogen . 2 and m is the mass flow rate of oxygen. = 1 represents a mixture under stoichiometric conditions, O2 ∅ < 1 represents a mixture with excess oxidizer, and > 1 represents a mixture with excess fuel [14]. ∅ ∅
2.1. H2 and OH2G Gas Properties 1 1 Hydrogen is a colorless and odorless gas with a molar mass of 2.02 g mol− , a density of 0.089 g L− 1 1 (at 25 ◦C and 1 atm), and higher and lower heat values of 142.18 kJ g− and 120.21 kJ g− , respectively. 1 The properties of OH2G at 25 ◦C are as follows: molar mass of 12.01 g mol− , a density of 1 0.49115 g L− , a volumetric ratio of 2:1 of H2 (66.6%) and O2 (33.34%), and upper and lower calorific 3 1 3 1 values of 12,751 kJ m− (142.18 kJ g− ) and 10,789 kJ m− (120.21 kJ g− ), respectively, which coincide with the values for pure hydrogen. The temperature of the adiabatic flame is 2107 ◦C and 2800 ◦C for hydrogen mixtures with air and oxygen, respectively [17,18]. The homemade water alkaline electrolyzer (WAE) is a dry cell system without a membrane between the electrodes, which has a common outlet for oxygen and hydrogen gases (oxyhydrogen gas), the ten electrodes are nickel-based, the connection is serial; PDM gaskets and alkali solution (NaOH, 5 wt%) were used. Its operation ranges are powered from 100 W–800 W and temperatures from 30 ◦C to 80 ◦C. A WAE was chosen because the device is one of the easiest ways for oxyhydrogen production, offering the advantage of simplicity and lower costs. In this study, the OH2G production Energies 2020, 13, 5526 4 of 11 system does not have the ability to compress the generated gas, and the system pressure is low at 1 atm. For this reason, the flow, pressure, composition, and temperature of OH2G at the burner inlet will depend directly on the operating conditions of the WAE, which include the operating power, electrolyte concentration, operating temperature, and time of WAE operation.
2.2. Procedure to Establish Dimensions of the Burner The area relationships, presented by Jones et al. [19], were used to establish the dimensions of the main sections of the burner and to calculate the optimal ratio between the injector area (Ai) and the throat area (At), Equation (3): A σ i = (3) At (σ + R)(1 + R)(1 + CL) in which, σ is the relative density of the gas mixture and R is the (air/fuel) drag ratio. Jones also calculated the relationship between the throat area (At) and the total area of the flame portholes (Ap), using Equation (4): At p = Cd 1 + CL (4) AP where CL and Cd are the friction loss coefficients generated in the gas as it flows through the burner sections. They have typical values between 30% and 60% considering a primary air composition (the portion of air required to complete combustion mixes with the gas before it reaches the burner port), OH2G has a 66.6–33.4% volumetric relationship in the fuel-oxidant premixing stage. At the top of the burner, the number of flame ports (Np) is defined as Equation (5) [19–21]:
. mmix Np = (5) ρ AP Vp mix ∗ ∗ To characterize the combustion requirements, the flame port design is optimized to define the gas flow rate characteristics before ignition. Important changes are observed if the geometry (Ap), flow rate . (mmix), density (ρmix), and gas velocity in the flame port (Vp) (without combustion) are modified as demonstrated in the continuity Equation (6) [21–23]:
. mmix Vp = (6) AP ρ ∗ mix Compared to research conducted with regard to hydrocarbon gas flame ports, limited studies have been performed on hydrogen or OH2G. Jones et al. [19] recommended a maximum spacing between ports of 6 mm, a depth/diameter ratio greater than two, a length in the mixing zone of 10 to 12 times the throat diameter (Dt), and a Dp = 0.80 mm for hydrogen/air mixtures. OH2G is produced under stoichiometric conditions ( = 1); thus, the risk of flashback increases. This is attributed to the difference ∅ between the gas velocity (Vp) and the combustion rate (SL) in the flame ports. In this case, Vp depends directly on the configuration of the flame port and SL is a function of the equivalence ratio ( ) in the 1 ∅ gas mixture, where the value of SL can be established to be within a range of 9.5–10.30 m s− according to studies on H2/O2 stoichiometric conditions [24–29]. Figure1 describes the method used for the development of the OH2G burner. Figure2 show the evaluation of the number of flame ports with respect to the OH 2G flow rate 1 from 0.5 to 4 sL min− (sL means liters to standard conditions at 25 ◦C and 1 atm) this flow was measured with the flow meter Alicat Scientific (which is special for oxyhydrogen flow and operating 1 range of 0-20 L min− ) and gas velocities in the flame port (Vp) were calculated for port diameters (Dp) 1 of 0.40, 0.50, and 0.60 mm. Figure2a shows the relationship between the OH 2G velocity (m s− ) and the number of ports. In this case, Dp is defined and the OH2G flow rate for each flame port is evaluated. The results correspond to Vp values higher than those found in the literature for a combustion velocity 1 of 9.50–10.30 m s− to guarantee the stability of the flames at each port. Energies 2020, 13, 5526 5 of 11 EnergiesEnergies 20 202020, 1, 31,3 x, xFOR FOR PEER PEER REVIEW REVIEW 5 5of of 11 11
Figure 1. Methodology for the development of OH2G burners. FigureFigure 1. 1. Methodology Methodology for for the the development development of of OH OH2G2G burners. burners. 1 Figure2b shows the OH 2G flow rate (sL min−−1) according to the diameter and number of defined FigureFigure 2b 2b shows shows the the OH OH2G2G flow flow rate rate (sL (sL min min−1) )according according to to the the diameter diameter and and number number of of defined defined ports. The OH2G flow rate represents the minimum flow rate required to guarantee that the developed ports.ports. The The OH OH2G2G flow flow raterate represent represents s thethe minimum minimum flow flow raterate requiredrequired to to guarantee guarantee that that the the velocity (Vp) of OH2G in each of the flame ports is greater than or equal to the OH2G combustion rate developeddeveloped velocity velocity ( V(Vp)p )of of OH OH2G2G in in each each of of the the flame flame ports ports is is greater greater than than or or equal equal to to the the OH OH2G2G (SL), to prevent the development of flashback in the generated flames. combustioncombustion rate rate ( S(SL),L), to to prevent prevent the the development development of of flashback flashback in in the the generated generated flames. flames.
( a()a ) ( b(b) )
FigureFigure 2. 2. ( a()a )OH OH2GG2G velocity velocity velocity ( ( VV(VPp)P) )and andand ( (b(bb)) )OH OHOH22G2GG flow flowflow rate, rate,rate, as asas a a afunction functionfunction of ofof the thethe number numbernumber of ofof ports portsports ( (N(NNpp)p.).) .
TheThe dimensions dimensions of of the the different different burner burner sections sections are are obtained obtained from from the the optimization optimization of of the the configurationconfiguration of of the the flame flame ports. ports. Figure Figure 3a 3a shows shows the the final final design design of of the the burner burner head, head, Figure Figure 3b 3b describesdescribes the the distribution distribution of of flame flame ports ports where where A A-A-A is is a across cross sectio section,n, L Lh his is the the head head length, length, L Lt ist is the the
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The dimensions of the different burner sections are obtained from the optimization of the configurationEnergies 2020, 13 of, x theFOR flame PEER REVIEW ports. Figure 3a shows the final design of the burner head, Figure3b describes6 of 11 the distribution of flame ports where A-A is a cross section, Lh is the head length, Lt is the burner length burner length total and Dc is a center diameter; and Figure 3c shows the cross section B, where are total and Dc is a center diameter; and Figure3c shows the cross section B, where are showed Dp and Lp showed DP and LP configuration of the flame ports in the burner head, a port diameter (DP1) of 0.50 configuration of the flame ports in the burner head, a port diameter (Dp1) of 0.50 mm and to a and mm and to a and length (LP1) of 1.60 mm in order to accelerate the flow to a velocity of 11.7 m s−1 are length (L ) of 1.60 mm in order to accelerate the flow to a velocity of 11.7 m s 1 are selected for a total selected pfor1 a total of 12 flame ports distributed in the burner head with a spacing− of 3 mm between of 12 flame ports distributed in the burner head with a spacing of 3 mm between ports, and (Dp2) of a ports, and (DP2) of a 1.5 mm and (LP2) of a 2 mm to direct the flow into the burner head, improving 1.5 mm and (L ) of a 2 mm to direct the flow into the burner head, improving stability of the flame. stability of thep 2flame.
(a) (b) (c)
FigureFigure 3.3.( (aa)) Final Final design design of of burner burner head, head (,b ()b Distribution) Distribution of of flame flame ports, ports, (c) (Dc)p DandP andLp configurationLP configuration of theof the flame flame ports ports in the in the burner burner head. head.
2.3.2.3. BurnerBurner EvaluationEvaluation inin thethe ExperimentalExperimental TestTest Module Module . The thermal efficiency of the burner (q) depends on the mass flow rate mOH G and Lower Calorific The thermal efficiency of the burner (q) depends on the mass flow rate2 푚̇ 푂퐻2퐺 and Lower ValueCalorific (LCV) Value of OH (LC2G,V) asof describedOH2G, as described in Equation in (7):Equation (7): 푞 =. 푚̇ ∗ 퐿퐶푉 q = m 푂퐻2퐺LCV 푂퐻2퐺 (7)(7) OH2G ∗ OH2G The thermal efficiency of a gas burner is defined as the percentage of the input thermal energy The thermal efficiency of a gas burner is defined as the percentage of the input thermal energy transferred to the desired load with respect to a time interval. In this case, the thermal efficiency is transferred to the desired load with respect to a time interval. In this case, the thermal efficiency determined by measuring the required time to produce an increment of 50 °C from the initial is determined by measuring the required time to produce an increment of 50 C from the initial temperature for a standard load of 1 kg of water as described in Equation (8): ◦ temperature for a standard load of 1 kg of water as described in Equation (8): (푚푤퐶푝푤 + 푚푅퐶푝푅)(푇2 − 푇1) 휂 = (8) mwCpw푚+̇ 푂퐻m2R퐺C∗pR퐿퐶푉(T푂퐻2 2퐺T1) η = . − (8) where mw and mR are water and container masses,mOH G respectively.LCVOH G Cpw and CpR correspond to the water 2 ∗ 2 and container-specific heats, respectively, T1 is the initial room temperature in the place of the where mw and mR are water and container masses, respectively. Cpw and CpR correspond to the experiment, and T2 is the final temperature of the water load, both temperatures were measured with water and container-specific heats, respectively, T is the initial room temperature in the place of the a thermometer. Figure 4 shows the experimental test1 module (ETM), which comprises the combustion experiment, and T is the final temperature of the water load, both temperatures were measured with chamber and oxyhydrogen2 gas production system. Figure 4a shows a photograph of the homemade a thermometer. Figure4 shows the experimental test module (ETM), which comprises the combustion ETM. Figure 4b shows a diagram of the ETM components. The OH2G production system comprises chamber and oxyhydrogen gas production system. Figure4a shows a photograph of the homemade a DC power source, WAE, recirculatory, bubbler, and dryer vessel. The combustion chamber includes ETM. Figure4b shows a diagram of the ETM components. The OH G production system comprises a a flame arrestor, burner, loading vessel, thermometer, and thermography2 camera. DC power source, WAE, recirculatory, bubbler, and dryer vessel. The combustion chamber includes a The thermal camera used for this experiment is a Fluke TiS 20 with a thermal resolution of 0.10 flame arrestor, burner, loading vessel, thermometer, and thermography camera. °C and a temperature range from −20 to 350 °C. This camera allows an automatic and uniform scaling, The thermal camera used for this experiment is a Fluke TiS 20 with a thermal resolution of 0.10 C with an image quality of 5 Mpx (Megapixels). The thermal camera was located at 30 cm from ◦the and a temperature range from 20 to 350 C. This camera allows an automatic and uniform scaling, burner head keeping perpendicularity− for◦ better image capture, in the same way, a tripod was used with an image quality of 5 Mpx (Megapixels). The thermal camera was located at 30 cm from the to provide stability and support the camera and avoid the vibrations in the photos. The hydrogen burner head keeping perpendicularity for better image capture, in the same way, a tripod was used percentage in oxyhydrogen gas flow was determined with a K1550 hydrogen analyzer, which to provide stability and support the camera and avoid the vibrations in the photos. The hydrogen operates in a detection range of 50–100% accuracy 2%, this device is ideal for measuring a high percentage in oxyhydrogen gas flow was determined with a K1550 hydrogen analyzer, which operates percentage of hydrogen in binary gases. in a detection range of 50–100% accuracy 2%, this device is ideal for measuring a high percentage of ± hydrogen in binary gases.
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Figure 4. (a) Photograph of the experimental test module for burner evaluation for open combustion, Figure 4. (a) Photograph of the experimental test module for burner evaluation for open combustion, (Figureb) Diagram 4. (a) ofPhotograph the experimental of the experimental test module. test module for burner evaluation for open combustion, ((bb)) Diagram Diagram of of the the experimental experimental testtest module.module. 3. Results and Discussion 3.3. ResultsResults andand DDiscussionsiscussions The thermal efficiency of OH2G burners is evaluated as a function of the oxyhydrogen gas flow rate.The The thermal hydrogenthermal efficiencyefficiency percentage ofof OHOH determined22GG burnersburners in is theis evaluatedevaluated oxyhydrogen asas aa functionfunction gas flow ofof rate thethe with oxyhydrogenoxyhydrogen the K1550 gasanalyzergas flowflow rate.wasrate. 66.65%.The The hydrogen hydrogen According percentage percentage to the WAE determined determined operating in in conditions the the oxyhydrogen oxyhydrogen and the burnergasgas flow flow design rate rate with with parameters, the the K1550 K1550 a minimum analyzer analyzer 1 1 wasandwas maximum 66.65%. 66.65%. AccordingAccording flow rate of to to 1.5 the the sL minWAEWAE− and operating operating 3.5 sL min conditions conditions− , respectively, and and the the were burner burner selected. design designFigure parameters, parameters,5a,b show a a minimumtheminimum shape andand maximum maximum configuration flow flow of rate rate the of of flames 1.5 1.5 sL sL min formin−1 the−1 and and WAE 3.5 3.5 sL sL minimum min min−1−1,, respectively respectively and maximum,, were were operatingselected. selected. Figure Figure flows 5respectively,5aa,,bb show show the the andshape shape the and and burner configuration configuration head thermography. of of the the flames flames for Thefor the the yellow WAE WAE colorminimum minimum of the and and flames maximum maximum is attributed operating operating to flowselectrolyteflows respectivelyrespectively traces (NaOH),, andand thethe and burnerburner water headhead drawn thermography.thermography. in by OH2G. TheThe Also yellowyellow shown colorcolor in the ofof thefigure,the flamesflames the temperatureisis attributedattributed tovaluesto electrolyte electrolyte reached traces traces in each (NaOH) (NaOH) zone and ofand the water water burner. drawn drawn in in by by OH OH22G.G. Also Also shown shown in in the the figure, figure, the the temperature temperature valuesvalues reachedreached inin eacheach zonezone ofof thethe burner.burner.
Figure 5. Oxyhydrogen gas flames developed in burner and thermography of burner surfaces in C, FigureFigure 55. . OxyOxyhydrogenhydrogen gasgas flamesflames developeddeveloped inin burnerburner andand thermographythermography ofof burnerburner surfacessurfaces inin °C,◦°C, for (a) minimum and (b) maximum flow rate. forfor ( (aa)) minimum minimum and and ( (bb)) maximum maximum flow flow rate rate. .
The length and thickness of the obtained flames depend on the OH2G flow rate supplied. TheThe lengthlength andand thicknessthickness ofof thethe obtainedobtained flamesflames dependdepend onon thethe OHOH22GG flowflow raterate supplied.supplied. TheThe The OH2G velocity in the flame port increases as the flow rate increases, and the combustion velocity OHOH22GG velocityvelocity inin thethe flameflame portport increasesincreases asas thethe flowflow raterate increases,increases, andand thethe combustioncombustion velocityvelocity remains constant to achieve flames of greater length and thickness. The purpose of the thermography remainsremains constant constant to to achieve achieve flames flames of of greater greater length length and and thickness. thickness. The The purpose purpose of of the the thermography thermography observation is to identify the flame heat distribution. The maximum temperature occurred on the observationobservation isis toto identifyidentify thethe flameflame heatheat distribution.distribution. TheThe maximummaximum temperaturetemperature occurredoccurred oonn thethe thinner surfaces of the burner supports. thinnerthinner surfacessurfaces ofof thethe burnerburner supports.supports. 3.1. Efficiency Tests 3.1.3.1. EfficiencyEfficiency TTestsests 1 In these tests, a flow rate range of 1.5 to 3.5 sL min− is considered. Figure6a shows a diagram of In these tests, a flow rate range of 1.5 to 3.5 sL min−1−1 is considered. Figure 6a shows a diagram the deviceIn these installation tests, a flow and rate instrumentation range of 1.5 to used 3.5 forsL themin tests, is considered Figure6b shows. Figure photograph 6a shows a of diagram the test ofof thethe devicedevice installationinstallation andand instrumentationinstrumentation usedused forfor thethe teststests,, FigureFigure 6b6b showsshows photographphotograph ofof thethe and Figure6c shows the thermographic results ( ◦C). testtest andand FigureFigure 6c6c showsshows thethe thermographicthermographic resultsresults (°C).(°C).
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Figure 6. Analysis system for efficiency tests: (a) Diagram of system, (b) Photograph of the test, FigureFigure 6. 6.Analysis Analysis system system for for efficiency efficiency tests: tests: (a () aDiagram) Diagram of of system, system, (b ()b Photograph) Photograph of of the the test, test, (c )( c) (c) Thermographic results (◦C). ThermographicThermographic results results (°C). (°C). Figure7a shows the variation in thermal e fficiency as a function of height (H). The thermal Figure 7a shows the variation in thermal efficiency as a function of height (H). The thermal efficiencyFigure of 7 thea shows burner the is a variation function ofinthe thermal distance efficiency between as the a burner function and ofthe height loading (H). vessel The thermal and the efficiency of the burner is a function of the distance between the burner and the loading vessel and efficiencyheat transfer. of the From burner the experimentalis a function results,of the distance an optimal between height the of 10burner mm betweenand the loading the burner vessel and and the the heat transfer. From the experimental results, an optimal height of 10 mm between the burner and theloading heat vesseltransfer. is From determined. the experimental Figure7b showsresults, the an dependenceoptimal height between of 10 mm the between thermal the e ffi burciencyner and thethe loading loading vessel vessel is isdetermined. determined. Figure Figure 7b 7b shows shows the the dependence dependence between between the the thermal thermal efficiency efficiency OH2G flow rate. andand OH OH2G2G flow flow rate. rate.
(a )( a ) (b ()b )
FigureFigure 7. 7.(a )(( aThermal)) Thermal efficiency efficiency efficiency as as a functiona function of of load load height, height, (b ( )b Thermal) Thermal efficiency efficiency efficiency as as a function a function of of OH G flow rate. OHOH2G2 Gflow flow rate rate
The results show an almost linear dependence between the OH2G inlet flow rate and the efficiency TheThe results results show show an an almost almost linear linear dependence dependence between between the the OH OH2G2G inlet inlet flow flow rate rate and and the the in the burner for a loading height, while the volume of available air between the burner and the load efficiencyefficiency in in the the burner burner for for a aloading loading height, height, while while the the volume volume of of available available air air between between the the burner burner remains constant. The burner efficiency is a function of the gas flow rate, which directly affects the andand the the load load rem remainsains constant. constant. The The burner burner efficiency efficiency is isa functiona function of of the the gas gas flow flow rate, rate, which which directly directly length and thickness of the flames. High gas flow rate produces larger flames; however, decreasing the affectsaffects the the length length and and thickness thickness of of the the flames. flames. High High gas gas flow flow rate rate produces produces larger larger flames; flames; however, however, distance between the flames and increasing the heat transfer (convection) reduces the effects caused by decreasingdecreasing the the distance distance between between the the flames flames and and increasing increasing the the heat heat transfer transfer (convection) (convection) reduces reduces the the the interaction between the flames and the secondary air. effectseffects caused caused by by the the interaction interaction between between the the flames flames and and the the secondary secondary air. air. 3.2. Analysis of Flames as a Function of the WAE Operating Time 3.2.3.2. Analysis Analysis of ofF lamesFlames as as a Fa unctionFunction of ofthe the WAE WAE O Operatingperating T imeTime Table1 shows the flames obtained in each of the tests performed over a period of 60 min. A drastic TableTable 1 1shows shows the the flames flames obtained obtained in in each each of of the the tests tests performed performed over over a aperiod period of of 60 60 min. min. A A change in the luminous zone of the flame (left to right) is observed as the test progresses. The change in drasticdrastic change change in in the the luminous luminous zone zone of of the the flame flame (left (left to to right) right) is isobserved observed as as the the test test progresses. progresses. The The the luminosity of the flame is attributed to the decrease in the volume of hydrogen and an increase in changechange in in the the luminosity luminosity of of the the flame flame is isattributed attributed to to the the decrease decrease in in the the volume volume of of hydrogen hydrogen and and an an the volume of water vapor in the mixture. The increment of water vapor in the gas mixture instigates increaseincrease in in the the volume volume of of water water vapor vapor in in the the mixture. mixture. The The increment increment of of water water vapor vapor in in the the gas gas mixture mixture instigatesinstigates a coolinga cooling of of the the flame, flame, thus thus causing causing a decreasea decrease in in temperature. temperature. A A decrease decrease in in the the thickness thickness ofof the the flames flames is isobserved, observed, although although the the length length of of the the flames flames shows shows insignificant insignificant change, change, which which is isdue due
Energies 2020, 13, 5526 9 of 11
a cooling of the flame, thus causing a decrease in temperature. A decrease in the thickness of the Energies 2020, 13, x FOR PEER REVIEW 9 of 11 Energies 2020, 13, x FOR PEER REVIEW 9 of 11 Energies 2020flames, 13, x FOR is observed, PEER REVIEW although the length of the flames shows insignificant change, which9 of is 11 due to the Energies 2020, 13, x FOR PEER REVIEW 9 of 11 decrease in the volume of hydrogen in the gas mixture (OH G-water vapor). Therefore, a flow rate of to the decrease in the volume of hydrogen in the gas mixture (OH2G-2water vapor). Therefore, a flow to the decrease in the volume1 of hydrogen in the gas mixture (OH2G-water vapor). Therefore, a flow to the decrease2.50 sL in min the−1 − volumeof OH 2ofG hydrogen is considered in the to begas the mixture optimal (OH operating2G-water condition, vapor). Therefore, because if a the flow electrolyzer rateto the of decrease 2.50 sL minin the−1 ofvolume OH2G of is hydrogen considered in theto be gas the mixture optimal (OH operating2G-water condition,vapor). Therefore, because aif flow the rate of 2.50 sL min−1 of OH2G is considered to 1be the optimal operating condition, because if the rate of 2.50works sL min at higher−1 of OH flow2G ratesis considered (3.5 sL min to− be),−1 excessthe optimal water vaporoperating is produced condition, and because errors are if the generated in electrolyrate of 2.50zer workssL min at higherof OH 2flowG is ratesconsidered (3.5 sL tomin be−1 )the, excess optimal water operating vapor is condition,produced andbecause errors if arethe electrolyztheer works data which at higher could flow result rates in (3.5 the flamesL min being−1), excess extinguished water vapor during is p theroduced test. and errors are generatedelectrolyz erin worksthe data at whichhigher couldflow ratesresult (3.5 in thesL minflame−1), beingexcess extinguished water vapor duringis produced the test. and errors are generated in the data which could result in the flame being extinguished during the test. generated in the data which could result in the flame being extinguished during the test. Table 1. OH G flames developed in the burner, obtained in each test. Table 1. OH2G flames developed2 in the burner, obtained in each test. Table 1. OH2G flames developed in the burner, obtained in each test. Table 1. OH2G flames developed in the burner, obtained in each test. Table 1. OH2GD escriptionflames developedDescription in the burner, obtained in each test. Ima Imagege Description Image Description Image
A drastic change inA the drastic luminous change inzone the of luminous the flame zone (top of the to flamebottom (top) is to A drastic change in the luminous zone of the flame (top to bottom) is observedA drastic aschange the test inbottom) theprogresses. luminous is observed This zone as is the dueof testthe to progresses. flamethe initial (top This buildto bottom is- dueup and to) is the observed as the test progresses. This is due to the initial build-up and dragobserved of the as electrolyte. the testinitial progresses. build-up andThis drag is due of theto the electrolyte. initial build-up and drag of the electrolyte. drag of the electrolyte.
The change in the luminosity of the flame is attributed to the decrease The change in the luminosity of the flame is attributed to the decrease inThe the change volume in ofthe hydrogen Theluminosity change and in of thean the luminosityincrease flame is in attributed of the the volume flame to is the attributedof water decrease to in the volume of hydrogenthe decrease and in thean increase volume of in hydrogen the volume and anof increasewater in vaporin the involume the mixture. of hydrogen The increment and an increase of water in vapor the volume in the ofgas water mixture vapor in the mixture.the volumeThe increment of water vaporof water in the vapor mixture. in the The gas increment mixture of instigatesvapor in the a cooling mixture.water of Thethe vapor flame,increment in the thus gas of causing mixture water vapora instigates decrease in the a coolingin gas mixture of the instigates a cooling of the flame, thus causing a decrease in temperatureinstigates a cooling. flame, of the thus flame, causing thus a decreasecausing ina decrease temperature. in temperature. temperature.
A decrease in the thickness of the flames is observed, although the A decrease in the thickness of the flames is observed, although the A decrease in the Athickness decrease of in the thicknessflames is ofobserved, the flames although is observed, the lengthA decrease of the in flames the thickness shows insignificant of the flames change, is observed, which although is due to the the length of the flamesalthough shows the insignificant length of the change, flames showswhich insignificant is due to the decreaselength of in the the flames volume shows of hydrogen insignificant in the change, gas mixture which (OHis due2G -towater the decreaselength of inthe the flames volumechange, shows of which hydrogen insignificant is due in to the the change, decreasegas mixture which in the (OHis volume due2G to-water ofthe decrease in the volume of hydrogen in the gas−1 mixture (OH2G-water vapor). Therefore, a flow rate of 2.50 sL min of OH2G is the2 optimal vapor).decrease Therefore, in the volumehydrogen a flow of rate hydrogen in theof 2.50 gas mixture insL the min gas (OH−1 of mixture2 OHG-water2G is(OH vapor).theG optimal-water −1 1 2 operatingvapor). Therefore, conditionTherefore, a. flow rate a flow of 2.50 rate sL of 2.50min sL−1 of min OH ofG OHis theG optimal is the operatingvapor). Therefore, condition a . flow rate of 2.50 sL min of OH− 2G is the2 optimal operating conditionoptimal. operating condition. operating condition.
If the electrolyzer works at higher flows (3.5 sL min−1) the increment of If the electrolyzer works at higher flows (3.5 sL min−1) the increment of If the electrolyzer works at higher flows (3.5 sL min−1) the increment1 of waterIf the electrolyvapor inz theer Ifworks gas the mixture electrolyzer at higher instigates worksflows at(3. a highercooling5 sL min flows of−1 )the (3.5the flame, sLincrement min thus− ) the of water vapor in the gas mixture instigates a cooling of the flame, thus causingwater vapor a decrease in theincrement ingas the mixture temperature of water instigates vapor of the ina cooling the flame gas mixture whichof the couldflame, instigates result thus a in causing a decreasecooling in the oftemperature the flame, thus of the causing flame a decrease which could in the result in thecausing flame a beingdecrease extinguished in the temperature during the of test.the flame which could result in the flame being extinguishedtemperature ofduring the flame the whichtest. could result in the flame the flame being extinguishedbeing extinguished during during the test. the test.
It is important to clarify that at this stage of the study, it is not possible to carry out tests with It is important to clarify that at this stage of the study, it is not possible to carry out tests with naturalIt is gas important in the designed to clarify burner,that at this because stage the of the port study diameter, it is isnot very possible small to and carry it wasout tests specially with natural gas in It the is important designed burner, to clarify because that at the this port stage diameter of the study, is very it is small not possible and it was to carry specially out tests with designednatural gas for inoxyhydrogen. the designed In burner, the research because group, the port a dual diameter burner isfor very oxyhydrogen small and and it was natural specially gas designed naturalfor oxyhydrogen. gas in the In designed the research burner, group, because a dual the burner port diameter for oxyhydrogen is very small and natural and it wasgas specially mixturesdesigned wasfor oxyhydrogen.already designed; In the the research results of group, the test a willdual be burner published for oxyhydrogen shortly. and natural gas mixtures wasdesigned already for designed; oxyhydrogen. the results In the of research the test will group, be published a dual burner shortly for. oxyhydrogen and natural gas mixtures was already designed; the results of the test will be published shortly. 4. Conclusionsmixtures was already designed; the results of the test will be published shortly. 4. Conclusions 4. Conclusions A burner4. Conclusions for the controlled combustion of OH2G produced in situ in an alkaline electrolyzer was A burner for the controlled combustion of OH2G produced in situ in an alkaline electrolyzer was designed,A burner manufactured, for the controlled and experimentally combustion of characterized. OH2G produced The inexperimental situ in an alkaline results electroly show a thermalzer was designed,A burner manufactured, Afor burner the controlled for and the experimentally controlled combustion combustion of characterized. OH2G produced of OH TheG producedin experimental situ in an in alkaline situ results in an electroly show alkaline a thermalz electrolyzerer was was designed, manufactured, and experimentally characterized.−1 The2 experimental results show a thermal efficiencydesigned, ofmanufactured, 30% for a minimum and experimentally flow rate of characterized.1.5 sL min −1 of The OH experimental2G and 76% for results a flow show rate a of thermal 3.5 sL efficiencydesigned, of 30% for manufactured, a minimum flow and rate experimentally of 1.5 sL min characterized.−1 of OH2G and The 76% experimental for a flow resultsrate of show3.5 sL a thermal efficiency−1 of 30% for a minimum flow rate of 1.5 sL min−1 of OH2G and 76% for a flow rate of 3.5 sL minefficiency−1 of OH of 230%G. The for uniquea minimum characteristics flow rate ofof 1.5oxyhydro sL mingen of areOH1 attractive2G and 76% as foran aalternative flow rate offuel 3.5 for sL 1 min−1 of OHeffi2ciencyG. The of unique 30% for characteristics a minimum flow of rateoxyhydro of 1.5 sLgen min are− ofattractive OH2G and as 76%an alternative for a flow rate fuel of for 3.5 sL min− applicationsmin−1 of OH in2G. open The combustionunique characteristics systems, either of oxyhydro as an enrichmentgen are attractive gas or substitute as an alternative in hydrocarbon fuel for- applicationsmin of OH 2inG. open The uniquecombustion characteristics systems, either of oxyhydro as an enrichmentgen are attractive gas or substitute as an alternative in hydrocarbon fuel for- derivedapplications gases, in foropen residential combustion and systems, industrial either applications. as an enrichment The performance gas or substitute of the OHin hydrocarbon2G burner is- derivedapplications gases, in foropen residential combustion and systems, industrial either applications. as an enrichment The performance gas or substitute of the inOH hydrocarbon2G burner is- subjectderived to gases, the WAE for residential operating andconditions industrial and, applications. if the electric The energy performance required of by the the OH electroly2G burnerzer isis subjectderived to gases, the WAE for residential operating andconditions industrial and, applications. if the electric The energy performance required of by the the OH electroly2G burnerzer is producedsubject to bythe a WAE renewable operating source conditions such as solar,and, ifnuclear, the electric hydroelectric, energy required ocean, wind,by the andelectroly so on,zer the is producedsubject to theby aWAE renewable operating source conditions such as solar,and, if nuclear, the electric hydroelectric, energy required ocean, bywind, the andelectroly so on,zer the is hydrogenproduced producedby a renewable is green. source such as solar, nuclear, hydroelectric, ocean, wind, and so on, the hydrogenproduced producedby a renewable is green. source such as solar, nuclear, hydroelectric, ocean, wind, and so on, the hydrogen produced is green. hydrogen produced is green.
Energies 2020, 13, 5526 10 of 11
of OH2G. The unique characteristics of oxyhydrogen are attractive as an alternative fuel for applications in open combustion systems, either as an enrichment gas or substitute in hydrocarbon-derived gases, for residential and industrial applications. The performance of the OH2G burner is subject to the WAE operating conditions and, if the electric energy required by the electrolyzer is produced by a renewable source such as solar, nuclear, hydroelectric, ocean, wind, and so on, the hydrogen produced is green. As the efficiencies of the systems are improved, the efficiency of the combustion systems will also increase; with further improvements being made to the electrolyte recirculation system and the drying process for oxyhydrogen gas. The efficiency results of the OH2G burner presented in this study can be compared with the values found in the literature that relates to the use of conventional hydrocarbon fuels (LP gas, methane, ethane, and propane) and the cost are similar because both atmospheric burners use the same materials in their manufacture. The main advantage of the OH2G burner is to eliminate the generation of carbon dioxide from the original natural gas burning to the emission of water steam from hydrogen combustion. This can be very attractive for industrial applications to meet environmental regulations.
Author Contributions: Conceptualization, R.d.G.G.-H. and J.M.S.-P.; methodology, R.M.-S.; validation, R.d.G.G.-H.; formal analysis, F.S.-M.; investigation, L.A.F.-H.; resources, R.d.G.G.-H. and J.M.S.-P.; writing—original draft preparation, J.M.S.-P.; writing—review and editing, R.d.G.G.-H.; visualization, L.A.F.-H.; funding acquisition, R.d.G.G.-H. and J.M.S.-P. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by Instituto Politécnico Nacional: Multigrid Project SIP 2024 (2019-2021), Innovation project ESIQIE (20196841 and 20200935), Innovation project ESIME Unidad Azcapotzalco (20196831 and 20200927), and CONACYT for the support provided for projects CEMIE Océano 249795 and Ciencia Básica A1-S-15770 (2019-2022). COFAA for the support granted. Acknowledgments: Roberto Moreno-Soriano and Froylan Soriano-Moranchel to thank the CONACYT for the scholarship assigned. Conflicts of Interest: The authors declare no conflict of interest.
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