Influence of heating oil formulation on the combustion and emissions

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Fossil Fuels

Influence of heating oil formulation on the combustion and emissions of domestic condensing boilers using fossil fuels and renewable fuels mixtures Claudia Esarte, and Jesús Delgado Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b00998 • Publication Date (Web): 04 Aug 2018 Downloaded from http://pubs.acs.org on August 10, 2018

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Energy & Fuels

Influence of heating oil formulation on the combustion and emissions of domestic condensing boilers using fossil fuels and renewable fuels mixtures Claudia Esarte*, Jesús Delgado Repsol Technology Center, C/Agustín de Betancourt s/n, 28935, Móstoles (Madrid), SPAIN. *Corresponding author: Phone: +34917531608. E-mail address: [email protected].

KEYWORDS Heating oil, biodiesel, energy efficiency, pollutant emissions, nitrogen oxide, condensing domestic boilers.

ABSTRACT

The residential sector is responsible for approximately 40% of final energy consumption in the EU, being a potential target to increase energy efficiency and to improve urban air quality. New high efficiency heating oil boilers have been developed requiring fuel adaption by diminishing the sulphur content in the fuel. The present work has led to conclude that further fuel

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development, including the use of alternative fuels, may be directed to reducing fossil fuel consumption and decreasing the formation of pollutants. Specific fuel properties such as distillation curve and nitrogen content show an influence on pollutant emissions, especially NOx, which can be reduced below the lowest limit required for gas domestic boilers, which until now set the state of the art in terms of NOx. emissions. The addition of renewable fuels in heating oil formulations, contributing to global CO2 decrease, does not affect the reduction in NOx emission as far as it does not affect nitrogen content and distillation curve of the fuel. Besides, a map of NOx emissions, useful to predict NOx emissions from latest generation heating oil boilers, independently on the type of fuel, has been inferred and an equation has been proposed to guarantee low NOx emissions depending on fuel properties.

INTRODUCTION

The building sector is responsible for 40% of final energy consumption and approximately 30% of the EU greenhouse emissions, being an important source of CO2 and atmospheric pollutants, which affect the local air quality. Consequently, European authorities are encouraging the substitution of old apparatus by modern equipment aiming to increase energy efficiency in buildings and to improve urban air quality. Promoting measures include requirements for high efficiency domestic boilers and encouragement of low emissions (CO, NOx and particles) equipment installation1,2. Lately, new heating oil boilers have been developed incorporating condensing technology, enabling the recovery of latent heat from water condensation in the exhaust gases, thus increasing energy efficiency. Traditional boilers lose a great amount of heat through the flue gases which are discharged at high temperature (150-250ºC)3; whereas condensing boilers


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Energy & Fuels

integrate a heat exchanger that favors the condensation of water vapor produced during combustion, recovering sensible and latent heat of flue gases. The condensing heat exchanger uses the return water from the heating circuit as the cooling medium to lower the temperature of flue gases below the dew temperature, recovering this way the latent heat of water vapor. This way the temperature of the return water is increased and thus less energy is necessary to reach the supply water temperature4. Modern blue flame burners are also integrated in such equipment, optimizing spray pulverization which results in combustion process improvement and emissions reduction. Besides, the exhaust gas is recirculated through circumferential holes or slits in the tube, resulting in a lower flame temperature and, thus, in a reduction of thermally formed NOx.5,6 The optimization of the energy use related to the incorporation of condensing technology and the improvement of the combustion process through the use of modern blue flame burners result in 10-15% energy efficiency increase3,4. Heating oil may contain high amounts of sulphur (i.e. some European countries admit up to 1000 mg/kge.g.7-12) that results into SOx emissions when heating oil is used in combustion processes. The combination of SOx emissions from the boiler exhaust gases with water from the condensation process, previously described, leads to water acidification and increases the risk of materials corrosion. Therefore, fuels need to be adapted to the new equipment by diminishing the sulphur content in order to avoid corrosion problems coming from water condensation. Further fuel development, including the use of biodiesel, may be directed to reducing fossil fuel consumption and decreasing the formation of pollutants. A significant number of recent studies related to fuel formulation effect, including biofuels, on the performance and pollutant emissions from diesel engines can be found in literaturee.g.13-17;


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also some papers address similar studies focused on heating and hot water production equipment, most of them related to gas and pellets boilers, sometimes focused on condensing boilers.4,18-24 Diesel oil is widely used as heating fuel25,26 and therefore, several studies focused on boilers or equipment for heat and hot water production using liquid fuels and biofuels have been found.27-45 The performance and the generation of pollutant emissions are addressed in such studies, focused on domestic boilers27-30, industrial or semi-industrial equipment, including furnaces,31-34,37 and experimental boilers and burners35,36,38-43. Although these studies address the performance and emissions of diesel heating oil and renewable liquid fuels in different equipment, there is a lack of such studies focused on diesel oil use and performance in condensing boilers. The results of the different cited scientific research works lead to dissimilar conclusions, given the different equipment, experimental conditions and fuels used in the experimental testing. Therefore, some authors observe an increase of NOx emissions when biodiesel is used as a fuel, both as a pure fuel or in combination with diesel, which is mainly attributed to the presence of unsaturated sites in the form of double bound in biodiesel structure that contributes to the formation of prompt NO.31,33,34,39,42 Whereas different research works report a diminish of NOx emissions related to the use of biodiesel, which is mainly attributed to the lowest content in nitrogen in fuel and to the lower combustion temperatures for biodiesel than for conventional diesel27,43. Furthermore, studies have been found in literature,32-34 addressing the influence of different fuel properties and combustion parameters on NO formation. These works point to the relevance of fuel properties such as density, cetane number or operation parameters, such as combustion pressure or fuel/air ratio on the formation of NO. General agreement is achieved regarding the influence of fuel composition on the emission of SO2, which strongly depends on the sulphur content in the fuel.

e.g.28,31,37-40

Besides, most of the


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works describe a reduction of CO and CO2 related to the use of biodiesel as heating fuel, given the higher carbon content in diesel as compared to biodiesel.e.g.31,37-40 Also some interesting observations are found, e.g., the regulation of the fuel pressure can lead to the complete combustion of diesel oil, minimizing the emission of some contaminants such as carbon monoxide.28,31,40 Most of the authors recommend biodiesel as a substitute for diesel heating oil, based on a potential diminution of pollutant emissions and a low or negligible impact of biodiesel on energy efficiency.e.g.27,28,37-40 In this context, Repsol, as a global energy company concerned about climate change and atmospheric pollutants, has studied the effect of fuel properties and composition on the performance and emissions of domestic heating oil condensing boilers using fossil fuels and different mixtures of fossil fuels and renewable fuels. Also, prediction equations of NOx emissions from these fuels and the influence of fuel parameters on emissions have been analyzed.

EXPERIMENTAL SECTION

The present study has been carried out using two commercial heating oil condensing boilers from different manufacturers and similar technical characteristics (Table 1). The air in both boilers is supplied by means of a forced draft fan. Boilers are equipped with blue flame burners, that are designed to minimize the emission of NOx by recirculating the exhaust gases through circumferencial holes or slits in the burner tube, resulting in a lower flame temperature and thus in a reduction of the thermally formed NOx. Fuel is fed by means of diesel oil pumps and pressurized conical nozzles with a spray angle of 80º, which operate at approximately 18 bar,


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optimizing the fuel pulverization. Boiler 1 burner is a modulating burner and controls the heating supply between 30 and 100% of nominal heating output by means of a modulating diesel oil pump. On the other hand, Boiler 2 allows heating supply at certified heating output and at 2/3 of nominal heating output by integrating a 2 stage diesel oil pump in the configuration of the burner. The experimental tests presented in this paper have been carried out at nominal heating output. Certified heating efficiency and heating output are similar for both boilers. Heating efficiency has been experimentally determined following European Standard EN 304:1994+A2:200446, which applies to the determination of the performance of heating boilers fired by liquid fuels, following the direct method. The tested boiler is integrated in a closed circuit for water heating (Figure 1), in which a heat exchanger is also included in order to simulate a real heating system, in which water is supplied at high temperature (70-80ºC) and returns at lower temperatures (50-60ºC). The water mass flow, as well as the temperature of water entering and leaving the system are measured. The difference between temperatures must be around 20ºC. Heating oil consumption is measured by means of a weighing vessel. The combustion process is set for an air-fuel equivalence ratio (λ) of 1,2 by adjusting the air and fuel inlet. This λ value has been fixed and set according to the manufacturers of the boilers data, which indicated that this is an optimal combustion point for this kind of tests. The test period is 60 minutes and intermediate results are taken at 30 minutes. In the direct method, heating efficiency of the boiler (η) is defined as the useful heat output (P) referred to the heat supply (QB) as in Equation 1. η = P/QB

(Equation 1)


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Energy & Fuels

The amount of useful heat output transmitted to the heat carrier (water) is measured in the boiler circuit by measuring the mass flow of cold water entering the boiler circuit and the rise of temperature between the outlet water temperature and the inlet water temperature. P = m1 x c1 x (TF-TE) in W

(Equation 2)

where m1: water mass flow (cold water entering the system/hot water leaving the system) in kg/s; c1: specific heat capacity of water at (TF+TE)/2, in J/(kg·ºC); TE: temperature of the entering cold water, in ºC TF: exit temperature of the water, in ºC The heat supply is calculated as follows: QB = BxNCV in W

(Equation 3)

where: B: mass flow of fuel oil, in kg/s; NCV: Net calorific value of fuel oil, in J/kg. The concentrations of O2, CO, NO, NO2 and SO2 in the exhaust gases have been measured by means of two Testo combustion and emissions analyzers (Testo 350 XL and Testo 330-2) which measurement uncertatinies are shown in Table 2. Particles are measured using an automatic Testo opacimeter. The study has been carried out consuming 6 samples of commercial heating oil (CHO), as defined by Spanish regulation,7 6 samples of commercial low sulphur diesel oil (LSDO); and 18 heating oil fuel samples formulated from 14 refinery products. Besides, different formulations using CHO and LSDO as base fossil fuels in combination with alternative fuels from 5 to


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50%v/v have been tested. The selected alternative fuel samples are fatty acid methyl esters commercially available and vegetable oils obtained from biodiesel producers. These samples have not been subject to any pre-treatment of transformation process for the purpose of this work. The main properties of fuels and fuel formulations in this study have been analyzed according to Table 4.

RESULTS AND DISCUSSION

The performance of different fuel samples including commercial test fuels, laboratory pilot heating oil formulations and alternative heating oil formulations has been tested in commercial heating oil condensing boilers. The results obtained in this experimental work are presented and analyzed as follows, based on the different type of fuel samples used. 1.

Commercial fuel tests

The performance of 6 samples of CHO and 6 samples of commercial LSDO has been studied in the two commercial heating oil condensing boilers, previously referred, installed in the experimental set-up as required by the test method.46 All the samples have been characterized according to Table 4. The most significant differences between these two groups of samples are related to the sulphur and nitrogen content in fuel, density and distillation curve. As it may be observed in Table 5, CHO samples present higher sulphur and nitrogen content values than LSDO samples, therefore higher emissions can be expected from CHO than LSDO samples. Besides, CHO samples have also higher density and distillation curve values than LSDO samples, which are desirable properties for heating fuels since high density implies high energy content per volume unit. The samples show values according to heating oil characteristics7-12 in the rest of parameters with no remarkable differences depending on each sample.


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Energy & Fuels

The obtained results in terms of heating efficiency and combustion emissions are similar for both boilers, since the equipment design and the technology are similar. Heating efficiency determined following EN 304:1994+A2:200446 are comparable for different fuels used, as observed previously by other authors,e.g.31,40 and results are in agreement with the ones certified by manufacturers and presented in Table 1. The concentrations of O2, CO, NO, NO2, SO2 and opacity have been measured in the exhaust gases. CO and opacity are independent of the tested fuel. CO emissions remain under 20 mg/kWh, which is under the toughest level established for CO emissions from domestic boilers (60 mg/kWh)37. Opacity also shows very low levels, presenting values near zero. These results on CO emissions and opacity might be related to the pressure at fuel nozzle that favors the complete combustion of fuel, as it has been observed in other works operating at similar pressure.28,31,40 SO2 emissions are directly related to the sulphur content in fuel, as it is shown in Figure 2, where two different SO2 emissions zones can be distinguished considering the sulphur content in fuel, corresponding to LSDO (low emissions) and CHO (high emissions). NOx emissions present dependence on the fuel, being lower for LSDO in comparison with CHO (Figure 3), as can be expected taking into account the lower content in nitrogen of LSDO samples (Table 5). It is noteworthy that NOx emissions from LSDO samples show values below or around 70 mg NOx/kWh, which is the most restrictive limit established for gas boilers (EN 26747). Gas boilers currently set the state of the art regarding NOx emissions limits; therefore, achieving such limit by means of the combination of certain heating oil formulations and the most advanced oil boilers is a remarkable finding.


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2.

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Laboratory pilot heating fuel formulations

Tests using commercial fuel samples reveal an obvious influence of fuel formulation on NOx emissions from the most advanced domestic heating boilers. NOx emissions are especially relevant to make gas and oil heating equipment equivalent in terms of emissions of pollutants. Thus, an analysis of the fuel characteristics that show an influence on such emissions has been carried out. The performance of 14 refinery streams and 18 pilot heating oil fuel samples formulated from such streams has been analyzed using only Boiler 1, given the similar results obtained for both apparatus in the previous tests. These pilot formulations have been designed targeting the maximization of energy density and minimization of nitrogen content in the fuel samples, with the intention of simulating the optimal heating oil formulations identified when studying the performance of commercial fuel samples. All the refinery streams and pilot heating oil formulations have been analyzed according to Table 4. As stated before, the results in terms of heating efficiency and combustion emissions are in agreement with those obtained for CHO and LSDO. Energy efficiency values are in agreement to the manufacturer certification. CO and opacity are independent of the tested fuel and show low concentrations, probably due to the pressure at fuel nozzle that favors the complete combustion of fuel28,31,40, and the concentrations of both contaminants are low referred to current emission limits. SO2 emissions are directly related to the sulphur content in fuel samples (Figure 4). Figure 5 shows NOx emissions from Boiler 1 consuming refinery product streams and pilot formulations. As it is seen in such figure, many of the refinery products lead to NOx emissions levels under or around the most restrictive levels established for gas boilers47, corresponding to refinery streams with low nitrogen content and low energy density. The highest NOx emissions


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Energy & Fuels

are associated to high energy density, as observed in previous works focused on biodiesel32, and high nitrogen content refinery products. NOx emissions from pilot formulations show values around the NOx limits for gas boilers since such formulations have been designed aiming for such level of emissions, keeping low nitrogen content, while maximizing advantageous properties related to heating oil, such as high density. The analysis of these results leads to conclude that the most appropriate refinery products for low emissions heating oil formulations are those with lowest nitrogen content and lowest density. These products are normally coming from low nitrogen crude oil and/or stream products from hydro-treating processes. In order to confirm the previous observations, NOx emissions results obtained so far have been statistically analyzed. The purpose of this analysis is to identify the most relevant fuel parameters for NOx formation in domestic heating oil condensing boilers and to correlate them to fuel properties. A multivariable analysis following multiple linear regression methodology has been performed considering NOx emissions as the dependent variable and fuel properties, gathered in Table 4, as explanatory variables. From this analysis NOx emissions are found to show a strong dependency on nitrogen content in fuel and distillation curve. A statistically representative prediction model of NOx emissions from heating oil condensing boilers as a function of nitrogen content and distillation curve has been inferred and validated from experimental data. The model has been assumed to be statistically robust since the normal probability plot of the residuals is approximately linear, supporting the condition that the error terms are normally distributed. Equation 4 represents the prediction model for NOx emissions as a function of nitrogen content and distillation curve:


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NOx = -11,336 + 0,173·N + 0,183·T95

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(Equation 4)

where: NOx: NOx emissions from domestic condensing heating oil boilers (mg/kWh) N: Nitrogen content in fuel (mg/kg) T95: Distillation curve. Temperature at which 95%v/v of fuel has been evaporated (ºC). From experimental data and the inferred prediction model, a map of NOx emissions from heating oil condensing boilers, as considered in this study, has been built (Figure 6). The map of emissions allows estimating NOx emissions from domestic heating oil condensing boilers as a function of the nitrogen content and distillation curve of the fired fuel. Three different areas depending on the level of NOx emissions can be distinguished in the plot. The lightest grey area corresponds to NOx emissions under 70 mg/kWh (limit set for gas boilers) which is the target level for the heating oil formulations in this study, thus a low NOx limit guarantee has been fixed. Heating oil formulations fulfilling parameters under the low NOx limit must satisfy Equation 5 to guarantee NOx emissions under 70 mg/kWh: (்ଽହିଶ଼଴) (ଵ଺ହିே)

3.

< 1,4082

(Equation 5)

Alternative heating fuel formulations

Finally, different formulations using fossil fuels as base fuels (CHO and LSDO) in combination with alternative fuels have been tested using Boiler 1. Alternative fuels, including biodiesel (fatty acid methyl esters) from different vegetable oils and used cooking oil, as well as, vegetable and used cooking oil (Table 3), have been mixed with CHO and LSDO at 2%v/v, 5%v/v, 10%v/v, 30%v/v and 50%v/v. Vegetable oil was mixed up to 10%v/v in both fossil fuel samples since it was not soluble at higher percentages. CHO, LSDO, alternative fuels and formulations have been characterized according to Table 4 and it can be stated that most of the samples fulfill the


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requirements for heating oil as required by current regulation7,48. The main results regarding sulphur and nitrogen content, density and distillation curve are shown in Table 6. Only used cooking oil and vegetable oil present density values above 900 kg/m3, however final formulation density decreases to heating oil levels when mixed with fossil fuels. It has to be noted that alternative fuels present low nitrogen and sulphur content, thus a reduction in both NOx and SO2 emissions could be expected. Nevertheless, even though distillation curve cannot be determined for alternative fuels, density, that is also an indicator of high molecular weight components, shows high values in alternative fuels, which could lead to higher NOx emissions as previously stated32. Energy efficiency tests have not been carried out with this kind of fuel formulations given that the equipment was not fully prepared for alternative fuels and long duration tests could be harmful. The results in terms of combustion emissions are in agreement with those previously observed in this work. CO and opacity are independent of the tested fuel and present low concentrations referred to current limitations and SO2 emissions are directly related to the sulphur content in fuel samples. SO2 emissions are reduced as compared to fossil fuels, this can be attributed to the lower sulphur content in alternative fuels in relation to conventional fuels, as observed by other authors.28,31,37 Once again, NOx emissions are the focal point of the obtained results because of their significant dependence on fuel formulation. As observed in Figure 7, when renewable fuel is added to fossil fuel from 10%v/v, NOx emissions decrease compared to pure fossil fuel emissions, reaching NOx reductions up to 25% when 50%v/v of alternative fuel is included in the formulation. Thus, it can be stated that renewable components contribute to the reduction of NOx emissions from heating oil domestic condensing boilers as compared to commercial heating oil. This reduction can be


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attributed to the lower content in nitrogen in the alternative fuels as compared to CHO, given that there is not a substantial variation of the distillation curve of the final formulation. Some authors also attribute the lower NOx emissions from biodiesel to the lower combustion temperatures for this fuel than for conventional diesel.27,43 There are no clear evidences of better candidates among the different tested alternative fuels to reduce NOx emissions. However, Biodiesel 1 and Biodiesel 4 samples appear to be the most appropriate for NOx reduction, whereas UCO is the less suitable, probably because it presents the highest density value. This observation confirms that not only nitrogen content but also density is relevant for NOx emissions from heating oil condensing boilers, as previously stated by other authors.32 On the other hand, when alternative fuels are mixed with low sulphur diesel oil, no significant advantage on the reduction of NOx emissions has been identified, and NOx emissions remain under the limit established for gas domestic boilers (Figure 8). This can be explained by the low nitrogen content in fossil and alternative fuels and the slight variation of the distillation curve of the final formulation as referred to fossil fuel. These observations reinforce the importance of nitrogen content in the fuel and indicate that distillation curve or density are not as relevant in this case. Again, there are no clear evidences of better candidates among the different tested alternative fuels to reduce NOx emissions, only UCO slightly increases NOx emissions when added in percentages over 5%v/v. Finally, aiming to validate the NOx prediction model and the map of emissions that have been inferred, the NOx emissions of the different formulations have been calculated by means of Equation 4. Real measurements have been compared to model predictions obtaining a


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Energy & Fuels

satisfactory correspondence, including formulations with UCO and vegetable oil, as it is shown in Figure 9.

CONCLUSIONS

The present work addresses the study of the performance and emissions of domestic heating oil condensing boilers using different liquid fuels, including fossil and renewable fuels. The main observations have led to conclude that liquid fuel properties, specifically distillation curve and nitrogen content, show an influence on NOx emissions from the fuel combustion in domestic latest generation heating oil boilers. With the appropriate fuel formulation, this pollutant may be reduced below the lowest limit required for gas domestic boilers, which until now set the state of the art in terms of NOx. It has also been observed that SO2 emissions are directly related to sulphur content in fuel formulation. CO emissions and opacity are independent of the tested fuels and both of them remain under the most restringing current limitations, these observations may be attributed to the use pressurized fuel nozzles that favor the complete combustion of fuel. Also heating efficiency is independent of the fired liquid fuel and is in accordance with the values certified by equipment manufacturers. These conclusions may also be applied when alternative fuels are integrated into heating oil formulations. It is remarkable that, given the low nitrogen and sulphur content in alternative fuels, when fossil fuel shows high sulphur and nitrogen content, the addition of alternative fuels to final formulation contributes to decrease NOx and SO2 emissions. In addition, a prediction model and a map of NOx emissions as a function of fuel properties, useful to predict NOx emissions from latest generation heating oil boilers, have been inferred and


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validated from experimental data. An equation as a function of nitrogen content and distillation curve is proposed to guarantee low NOx emissions when fuel is used in heating oil condensing boilers including blue flame burners, as the ones used in this study. The prediction model and therefore, the map of NOx emissions, have been validated for the use of fossil fuels and biodiesel mixtures up to 50% v/v. There are no clear evidences of better candidates among the selected alternative fuels to reduce pollutant emissions, even though biodiesel samples appear to be more appropriate than vegetable oil or used cooking oil.


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FIGURES

Figure 1. Schematic of the experimental set up.

50 Boiler 1 Boiler 2

40

SO2 (ppmv)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

30

20

10

0 0

100

200

300

400

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600

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S content in fuel (mg/kg)

Figure 2. SO2 emissions from Boiler 1 and 2 consuming commercial heating oil (CHO) and low sulphur diesel oil (LSDO) samples as a function of sulphur content in fuel


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Energy & Fuels

160 Boiler 1 Boiler 2 NOx Heating oil limit (EN-267)

140

NOx Gas limit (EN-267)

NOx (mg/kWh)

120 100 80 60 40 20

--

- Sa mple 6

- Sa mple 5

LSD O

- Sa mple 4

LSD O

- Sa mple 3

LSD O

- Sa mple 2

LSD O

- Sa mple 1

LSD O

- Sa mple 6

LSD O

- Sa mple 5

CHO

- Sa mple 4

CHO

- Sa mple 3

CHO

CHO

CHO

CH O-

Sam ple 1 - Sa mple 2

0

Figure 3. NOx emissions from Boiler 1 and 2 consuming commercial heating oil (CHO) and low sulphur diesel oil (LSDO) samples.

1000

800

SO2 (ppmv)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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600

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0 0

2000

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10000 12000 14000 16000 18000

S content in fuel (mg/kg)

Figure 4. SOx emissions from Boiler 1 consuming refinery products and pilot heating oil fuel samples related to fuel sulphur content


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180 Refinery product streams

Pilot heating oil formulations

160

NOx Heating oil limit (EN-267) NOx Gas limit (EN-267)

140

NOx (mg/kWh)

120 100 80 60 40 20

St Strea Stream 1 Stream 2 Stream 3 Stream 4 Stream 5 Stream 6 S re m St tream 7 Streaam 8 Stream 19 Stream 10 Fo Stream 11 Form ream 12 Formulatm 13 Formulation 4 Formulation 1 Formulation 2 Formulation 3 Formulation 4 F rmula ion 5 Foormulatio 6 Form ulation 7 n Formulat tio 8 n Formulation 9 Formulation 10 Formulation 11 Formulation 12 Formulation 13 Formulation 14 rmula ion 15 ul tio 1 at n 6 io 17 n 18

0

Figure 5. NOx emissions from Boiler 1 consuming refinery products and pilot heating oil fuel samples.

380 NOx (mg/kWh)

Distillation curve T95 (ºC)

360 70,00 120,0

340 Non available data Low NOx limit guarantee

320

300

280 0

50

100

150

200

250

300

350

400

450

500

N content (mg/kg)

Figure 6. NOx emissions map as a function of nitrogen content and distillation curve (T95).

160 Biodiesel 1 Biodiesel 4 Biodiesel 2 UCO Biodiesel 3 VO NOx Heating Oil limit (EN 267) NOx Gas limit (EN 267)

140

NOx Emissions (mg/kWh)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

120

100

80

60

40

20

0 0

2

5

10

30

50

Alternative Fuel (% v/v)


19

Energy & Fuels

Figure 7. NOx emissions from heating oil formulations using CHO as base fuel and different alternative components.

120

NOx Emissions (mg/kWh)

Biodiesel 1 Biodiesel 4 Biodiesel 2 UCO Biodiesel 3 VO NOx Heating Oil limit (EN 267) NOx Gas limit (EN 267)

100

80

60

40

20

0 0

2

5

10

30

50

Alternative Fuel (% v/v)

Figure 8. NOx emissions from heating oil formulations using LSDO as base fuel and differente alternative components.

150 140 130

NOx real measurements (mg/kWh)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 28

2

120

R =0,9816

110 100 90 80 70 60 50 40 30 20 10 0 0

10

20

30

40

50

60

70

80

90 100 110 120 130 140 150

NOx estimated values (mg/kWh)

Figure 9. NOx emissions real measurements versus NOx emissions estimated values by means of the developed prediction model.


20

Page 21 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

TABLES

Table 1. Technical characteristics of heating oil condensing boilers Boiler

Model Tifell Biofell 30 Wolf COB-29

1 2

Heating Output (kW)

Heating Efficiency (%)

30

98

29

97

Burner Blue flame Modulating Blue flame 2 Stages

Table 2. Gas analyzers measurement uncertainty. Parameter Oxygen (%v/v) CO (ppmv) NO (ppmv) NO2 (ppmv) SO2 (ppmv) Gases temperature (ºC)

Uncertainty 0,08 20 2 3,6 2 2

Table 3. Alternative fuels information Biodiesel origin Sample Name Biodiesel 1 Biodiesel 2 Biodiesel 3 Biodiesel 4 Vegetable oil (VO) Used Cooking Oil (UCO)

Rape (%v/v)

Soybean (%v/v)

2,5 20,2 18 0 5 81 1,5 84,5 Oil samples 18 0 0 0

Palm (%v/v)

Used cooking oil (%v/v)

Jatropha (%v/v)

23,2 47 14 14

54,1 0 0 0

0 35 0 0

47 0

0 100

35 0


21

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 28

Table 4. Analyses of fuels and formulations Property Density at 15ºC Distillation curve Nitrogen content Sulphur content Carbon and hydrogen content FAME content Aromatics content Net Calorific Value (NCV) Viscosity at 20ºC and 40ºC

Test Method ASTM D4052 ASTM D86 ASTM D4629 ASTM D5453 XRF UNE EN 14078 UNE EN 12916 ASTM D 240 ASTM D445

Table 5. CHO and LSDO properties N content (mg/kg)

Density (kg/m3)

Distillation Curve, T95* (ºC)

CHO Sample 1

S content (mg/kg) 710

250

854,5

372,3

CHO Sample 2

690

112

849,0

365,4

CHO Sample 3

590

237

856,4

379,6

CHO Sample 4

720

267

381,3

CHO Sample 5

620

245

857,2 853,4

CHO Sample 6

790

421

862,8

378,9

LSDO Sample 1

11

18

845,6

361,2

LSDO Sample 2

14

45

853,9

362,6

LSDO Sample 3

45

58

850,7

365,3

LSDO Sample 4

19 4

848,9 837,9

363,3

LSDO Sample 5

30 25

Sample Name

380,5

359,4

LSDO Sample 6 2 838,6 14 356,6 *T95: Temperature at which 95%v/v of fuel has been evaporated (ASTM D86)


22

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Energy & Fuels

Table 6. CHO and LSDO base fossil fuels and alternative fuels properties

Base fuel: CHO

S content (mg/kg) 636

N content (mg/kg) 393

Density (kg/m3) 875,7

Distillation Curve, T95* (ºC) 372,3

Base fuel: LSDO

16

45

853,5

359,5

Biodiesel 1

6

23

882,4

-

Biodiesel 2

10

20

878,9

-

Biodiesel 3

7

18

877,8

-

Biodiesel 4

0

4

883,6

-

VO

44

64

903,3

-

Sample Name

UCO 2 18 922,3 *T95: Temperature at which 95%v/v of fuel has been evaporated (ASTM D86)

AUTHOR INFORMATION Corresponding Author *Claudia Esarte Repsol Technology Center, C/Agustín de Betancourt s/n, 28935, Móstoles (Madrid), SPAIN. Phone: +34917531608. E-mail address: [email protected]. ACKNOWLEDGMENT The authors express their gratitude to Innovation Norway for partially funding the project through the European Economic Area Grant ES02-0166 awarded. ABBREVIATIONS CHO, Commercial Heating Oil; FAME, Fatty Acid Methyl Esther; LSDO, Low Sulphur Diesel Oil; NCV, Net Calorific Value; UCO, Used Cooking Oil; VO, Vegetable Oil.


23

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 28

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(46) European Standard EN 304:1994+A2:2004. Heating Boilers. Test Code For Heating Boilers For Atomizing Oil Burners. (47) European Standard EN 267:2000+A1:2011. Automatic Forced Draught Burners For Liquid Fuels. (48) European Standard EN 14214:2013 V2 + A1:2018. Liquid petroleum products - Fatty acid methyl esters (FAME) for use in diesel engines and heating applications - Requirements and test methods.


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Influence of heating oil formulation on the combustion and emissions

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