An Environmentally Friendly Configuration for Ammonium Nitrate

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An environmentally friendly configuration for ammonium nitrate decomposition azadeh mirvakili, samaneh bahrani, and Abdolhosein Jahanmiri Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/ie4016057 • Publication Date (Web): 13 Aug 2013 Downloaded from http://pubs.acs.org on August 19, 2013

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Industrial & Engineering Chemistry Research is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

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Industrial & Engineering Chemistry Research

1. Introduction:

Nitrate contamination of groundwater due to the excessive use of fertilizers in crops, livestock, sewage waste and septic tanks is a growing environmental concern facing mankind during past few decades

1-4

. The eutrophication of rivers and deterioration of water sources, as well as

hazards to human health are some serious problems caused by discharging nitrogen compounds into the environment 5. Drinking water containedexcessive nitrate can cause cancer and other diseases 6.According to World Health Organization (WHO), the amount of nitrate in drinking water should not be more than 50mgL−1 and European Community recommends levels of 25mgL−17, 8. So it is necessary to reduce nitrate concentration before discharging. The rising trend of nitrate concentrations lead to focus on denitrification process as the most effective method for its in situ removal, in which nitrate is transformed to nitrogen gas and removed from water. Recently, many different technologies have been developed for denitrification in order to solve the problem of NO3in drinking water or wastewater, e.g., membrane reactors electrochemical systems

14

, fluidized-bed reactors

15, 16

and fixed-bed reactors

17-19

9-13

, bio-

.Ammonium

nitrate as an important fertilizer with 34% nitrogen is one of themain sources of nitrate in soil. Because of the high solubility of nitrate in water, ammonium nitrate is a cause of groundwater contamination which is also present in some industrial waste water. For example, yellowcake dissolution in nitric acid, followed by a solvent extraction process is a common first stage of natural uranium production. After solvent extraction, the nuclear-pure uranyl nitrate solution is mixed with ammonia to precipitate uranium as ammonium diuranate (ADU). ADU filtrate contains ammonium nitrate as well as some quantities of radioactive impurities. This waste liquid stream poses a disposal problem owing to its high nitrate content and associated residual radioactivity. Waste water from washing of yellowcake contains a large amount of ammonium

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nitrate (75000-200000 ppm)

20

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, so denitrification process is necessary to decompose AN.

Although there are many processes for AN decomposition, in this study thermal decomposition is investigated. 1.1.Ammonium nitrate thermal decomposition: Several studies have been focused onammonium nitrate decompositionmechanism in literature 2126

. Since the observed thermolysis of ammonium nitrate is highly dependent on the

temperature,different mechanisms have been proposed. Decomposition of ammonium nitrate based on different temperature ranges, can follow various modes of reaction, as below 20, 24-26:

G573,1  12.94 kJ / mol

(1)

230 C NH 4 NO3 170   N 2O  2H 2O

G573,1  288.84 kJ / mol

(2)

3 1 230 C NH 4 NO3   N 2  NO2  H 2O 4 2

G573,1  379.39 kJ / mol

(3)

1 260 C NH 4 NO3   N 2  O2  2 H 2O 2

G573,1  413.63 kJ / mol

(4)



C NH 4 NO3 169   NH 3  HNO3



These 4 reactions are carried out at different temperatures. The first two reactions are performed at lower temperatures 27-29, while the last two are more favored at higher temperatures. At higher temperatures, AN decomposition is more likely to occur as in Eq (4). Gibbs free energy changes for all four reactions were determined at 300 °C and 1 atm20. Reaction (4) has the most negative Gibbs free energy change. Hence, this is the most probable reaction thermodynamically. Although there are few studies on thermal decomposition of ammonium nitrate, Bhowmicket al. considered a steady-state parametric study recently. It was found that the ammonium nitrate conversion enhances with an increase in the reactor temperature and feed concentration. They


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compared the model predictions with experimental data from a bench scale plant and results showed that the model predictions were consistent with the experimental measurements 20.

In thermal denitration process, nitrate stream is sprayed into a hot fluidized bed maintaining at the desired temperature by an induction heating system. In this process, ammonium nitrate decomposes predominantly into nitrogen, oxygen and water vapor, then small amounts of NOxforms as below 30: O 2  N 2  2 NO

(5)

1.2.NOx emission: Nitrogen oxides (NOx) as pollutants accompanying in combustion processes, lead to formation of acidic rain and photochemical smog. In the presence of sunlight, NOx and volatile organic compounds in the atmosphere react to form ground-level ozone as a major component of smog in the cities and in many rural areas as well. Although ozone is a protective layer high above the earth, the ozone that we breathe at ground level is the main cause of respiratory diseases and other health problems. Control of NOx emission remains to be one of the greatest challenges in environmental catalysis since the conventional three-way catalysts are no longer effective to reduce NOx under lean-burn conditions. Selective catalytic reduction (SCR) of NOx with hydrocarbons has become one of the most promising ways to solve this problem

31

. Vanadia

based catalysts are the most widely used catalysts for the SCR process owing to their high efficiency. Recently, selective catalytic reduction (SCR) of NO with NH3 has attracted remarkable attention from environmental view point

32

.Chaeet al. studied the reaction kinetics

over a V2O5-WO3/TiO2 catalyst which can describe the NH3 slip from a selective catalytic reduction (SCR) reactor as well as the maximum conversion of NO over wide range of reaction temperatures 33.



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1.3. Objectives In this study, improving ammonium nitrate thermal decomposition and reducingNOx production in the novel configuration named OCFFDRare the main goals. A mathematical modeling for ammonium nitrate thermal decomposition in this novel configuration is developed and the operating conditions have been optimized. Then the results have been

1 260 C NH 4 NO3   N 2  O2  2 H 2O 2

(6)

At high temperatures, nitrogen reacts with oxygen and NOx will be produced: O 2  N 2  2 NO

(7)

This work presents a novel configurationcalledOCFFDR in which not only AN conversion increases but also NOx amount decreases as an undesired product.

2. Process description: 2.1. Conventional reactor (FR)

A schematic diagram of FR configuration is illustrated in Fig. 1(a) which is a fluidized bed reactor used for the ammonium nitrate decomposition. The bed including sand, aerates from bottom and air fluidizes the sand in the bed. Sand and the air are heated by a heating source outside the bed. Indeed, the ammonium nitrate decomposition reaction as a thermal reaction


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without needing catalyst takes place on the hot sand surface predominantly. Liquid stream including ammonium nitrate produced during the other chemical processes is sprayed to the fluidized bed. The liquid droplets are deposited on the hot surface of emulsion particles and they vaporized due to high emulsion particles temperatures. Therefore, liquid ammonium nitrate is vaporized in the emulsion phase. High rate of heat transfer from the particles to the deposited droplets causes complete water evaporation and ammonium nitrate volatilization in the spray zone. NOx is formed during ammonium nitrate thermal decomposition in the presence of producednitrogen and oxygen and the hot air in FR.

2.2. OCFFDR Configuration:

Fig. 1(b) shows the OCFFDR configuration for ammonium nitrate thermal decomposition. In brief, this dual-type reactor includes two cascading fluidized bed and the fixed bed reactors. The fluidized bed is similar to FR which ammonium nitrate decomposition occurs in. The products of ammonium nitrate decomposition are emitted to air in the FR. Hence, the products of the fluidized bed rector in OCFFDR are sent to the second reactor. The second reactor is a catalytic fixed bed reactor packed with V2O5-WO3/TiO2 catalyst for a selective catalytic reduction of NO with NH3. In this reactor, water coolant temperature is 300°C because the optimum temperature for selective catalytic reduction of NO with NH3 varies in the range of 300 to 350 °C

32

. Two

layers of tubes exist in the fixed bed reactor. Air enters inner layer of tubes from the bottom and its temperature increases due to preheating for consuming in the fluidized bed reactor. Outer tube packed with the catalysts is the reaction side. Since the reactions are exothermic, water in the shell side cools the reaction side. Figure1



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3. Mathematical model 3.1. The reaction kinetics:

Two reactions take place in the fluidized bed reactor, simultaneously: ammonium nitrate decomposition and nitrogen oxide (NO) formationwhich are two exothermic and endothermic reactions, respectively. These reactions are as follows: 1 NH 4 NO3  N 2  O2  2 H 2O 20 2

(8)

O 2  N 2  2 NO 30

(9)

The following reaction rate equations are used: rAN  K 0 exp(  E / RT ) C AN 20

K 0  4.55  107

(10)

1 KJ KJ E  102.6 H rxn  118.86 s mol mol

rNO  aT CN2 CO2

1

2

T

1

2

exp(  E / RT ) 30 (11)

aT  1.32  1010

m 3   (mol K )  

1

2

s

E  545

KJ mol

The SCR process is mainly based upon the following two reactions in the fixed bed reactor32: 4 NO  4 NH 3  O2   4 N2  6H 2O

(12)

4 NH 3  5O2   4 NO  6H 2O

(13)


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And the reaction rate equations are as below:

 rNO 

k NO K NH 3 CNOCNH3 1  K NH 3 CNH 3

 rNH3 

k NO K NH3 CNOCNH3 1  K NH3 CNH3



k NH 3 K NH 3 CNH3 1  K NH CNH 3

H rxn  1888.4

KJ Kmol.K

(14)

H rxn  1164.6

KJ Kmol.K

(15)

3



k NH3 K NH3 CNH3 1  K NH3 CNH3

The kinetic parameters are presented in Table 1.

Table 1

3.2. Mathematical model of FR: The following assumptions are made in the mathematical modeling of the fluidized bed reactor:

(1) The mixture of atomizing air and droplets had a very high velocity at nozzle outlet. (2) Atomizing air detached from the jet as jet bubbles. (3) Radiative heat transfer from the fluidized bed to the solution droplets can be neglected. (4) Therefore, vaporization of ammonium nitrate inside the jet is quite unlikely due to very small residence time of the droplets. (5) Jet bubbles do not contain any ammonium nitrate vapor and can be treated the same as distributor bubbles. (6) Ammonium nitrate vapor is released into the emulsion phase, and its initial concentration in the emulsion phase is CeAN,0= mAN/(MANumfAc). (7) Decomposition of ammonium nitrate in the spray zone is neglected.



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(8) Due to rapid mixing, the operation is assumed to be isothermal which means that the bubble and the emulsion phases have the same temperature. (9) Both phases have the plug flow regimes. (10)

Gas flow through the emulsion phase remains constant at the minimum

fluidization velocity. (11)

Steady state condition exists.

(12)

The heat of vaporization of water is neglected. Δz

T

tial equations

describing mass and energy balances in the axial direction of FRare discussed in the following subsection: Mass balance equation for the bubble phase is:

 

2 Qi dCib    .kbei .(Cie  Cib )   . . rbji  0 Ac dh j 1

i  1,2,3,4,5

(16)

And the mass balance equation for the emulsion phase is so:

 (1   ).

2 Qi dCie .  (1   ). rij   .kbei .(Cib  Cie )  0 Ac dh j 1

i  1,2,3,4,5

(17)

The energy balance in the reaction zone is as follows:

2

2

j 1

j 1

(1   )   rj  (H fj )     . rb j  (H fj ) 

mi dT  Cp 0 Mi dh

i=1 to 5; i=1: AN; i=2: N2; i=3: O2; i=4: NO; i=5: H2O The input data are presented in Table 2.

Table 2


(18)

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3.3. Mathematical model of OCFFDR: The first reactor is fluidized bed and the mathematical model for this reactor is similar to FR. In order to simulate the fixed bed reactor in this research, the following assumptions have been applied: 

The gas mixture is considered as an ideal gas.



The case is investigated at steady-state conditions.



Axial diffusion of mass and heat are negligible because of the high gas velocity.



Plug flow pattern is employed in the reaction side.



The chemical reactions occur only on the catalyst particles.



The reactor is assumed to be adiabatic.

The mass and energy balance equations for the fixed bed reactor are expressed by Eq. (19) and (20), respectively:





F dy  av c k g ( y s  y )  0 Ac dz F Ac

Cp

dT dz

 av h f (T s  T ) 

(19)

Di Ac

(20)

U Shell (TShell  T )  0

Where y represents the phase mole fraction and T is temperature. Boundary conditions for the gas phase in the conventional reactor are expressed as:

z  0, y  yin , T  Tin

(21)

The mentioned mass and energy equations for the catalyst pellets are so:

av c k g ( y  y s )  ri  b  0

(22)



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(23)

N

av h f (T  T s )   b ri (H f ,i )  0 i 1

Table 3 presents the input data for the fixed bed reactor.

Table3

The correlations for physical properties, mass and heat transfer coefficients are listed in Supporting Information (S1) as well as hydrodynamic properties in Supporting Information (S2).

3.4. Pressure drop In order to calculate the pressure drop along the reactor, the Ergun momentum balance equation has been used as follows:

(1   ) 2  u g (1   ) u g  dp  150  1 . 75 dz  3d p  3 d p2 2

(24)

Where the pressure drop is in Pa. 4. Optimization

The goal of optimization is to find the values of decision variables which provide the maximum or minimum values for one or more desired objectives 34. DE method is an exceptionally simple, b

z

’

true global optimum 35.DE methodwas extensively studied in the previous publications 35-41. 4.1Objective Function and Constraints

The objective of this study is minimizing the ammonium nitrate and nitrogen oxide concentrations exiting FR. Hence, the objective function is defined as follows:


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F  CAN  CNO

(25)

Three decision variables including the fluidized bed temperature (T1), the gas velocity (ug) and the fixed bed temperature (T2) are considered during the optimization process. The ranges of decision variables are:

580  T1  680 K

(26)

2 U mf  U g  7 U mf

(27)

573  T2  623 K

(28)

The temperature of the fluidized bed should be less than 680 and upper than 580 K. The gas velocity range is 2Umf to 7Umf 20 and the temperature of the fixed bed can vary from 573 to 623 K 32

. Thus, constraints are considered as equations (26)-(28).

All constraints are considered during the optimization process. A penalty function method has been used to omit the unacceptable results automatically. In this study, 10 5 is considered as the penalty parameter, however this parameter depends on the order of magnitude of the decision variables. The objective function that should be minimized is:

6

OF  F  105  Gi

(29)

2

i 1

Where;

G1  max( 0, (T1  680))

(30)

G2  max( 0, (580  T1 ))

(31)

G3  max( 0, (U g  7U mf ))

(32)



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G4  max( 0, (2U mf  U g ))

(33)

G5  max( 0, (T2  623))

(34)

G6  max( 0, (573  T2 ))

(35)

The set of abovementioned differential-algebraic equations (DAE) are developed for OCFFDR modeling. The energy balances and mass balances for the reactor are developed. Moreover, these equations are coupled with non-linear algebraic equations of the kinetic model, transport property correlations and other auxiliary correlations. A backward finite difference approximationhas been applied to solve the set of equations. The optimization results are presented in Table 4. Table 4

5. Result: Thermal decomposition of AN occurs in the fluidized bed reactor of OCFFDR. Therefore to evaluate its performance, results for the first reactor of OCFFDR are compared with FR at first. Fig. 2(a) illustrates AN concentration profile along the reactor in both OCFFDR and FR configurations. A remarkable difference between AN concentrations in two configurations can be seen. The high rate of ammonium nitrate decomposition leads to more AN conversion or reduction of ammonium nitrate concentration along the bed. AN concentration decreases sharply in OCFFDR due to high bed temperature and gas velocity (Gas velocity is considered as the ratio of gas velocity to the minimum fluidization velocity).Fig. 2(b)shows how NO concentration changes along FR and fluidized bed reactor in OCFFDR. As depicted, the NO concentration increases considerably in the first reactor of OCFFDR in comparison to FR due to high bed temperature and inlet air velocity. The optimum velocity of inlet air (in OCFFDR) is 5 Umf while


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it is 2 Umf in FR configuration. NO production in fluidized bed reactor of OCFFDR is almost 2 times more than in conventionalFR and NO and other produced gases are sent to the second reactorof this configuration for SCR process. While,theproducts of FR emit to the atmosphere containing approximately 10 mole percent NO as an undesired material. N2 is another component produced while AN thermal decomposition. Although N2 is formed as a result of AN decomposition, it is not the only source. While fluidizing the reactor with air, N2 enters the reactor. As illustrated in Fig. 2(c), the initial concentration of N2 in the reactor is nonzero and it increases at the beginning of the reactor. Gradually it decreases in both configurations. At first, N2 concentration increases due to high AN thermal decomposition. By raising reactor temperature as a result of exothermic decomposition of ammonium nitrate, N2 and O2 reacts and NO is produced. So, N2 concentration decreases. Fig. 2(d) shows concentration profile of O2 which varies in the same trend as N2. Fig. 2(e)describes water concentration in OCFFDR as well as FR configuration. As seen in Fig. 2(e), the initial concentration of water is zero and the only source of water is the AN decomposition. Water concentration increases at first and after a while, it becomes constant because of the decline in the AN reaction rate along the reactor. This figure demonstrates remarkable water concentration in OCFFDR compared to FR due to operating under optimum conditions. This trend is also seen for other AN decomposition products such as N2 and O2 in Fig.2 (c) and (d).

Figure 2

AN conversions and NO mole percents in FR and fluidized bed reactor of OCFFDR are presented in Fig. 3(a) and (b), respectively. The AN conversions are 42% and 98% and NO mole percents are 8% and 14% in FR and OCFFDR, respectively. These two figures demonstrate



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greater AN conversion and accordingly NO mole percent in OCFFDR compared with FR as a result of operating at optimum conditions.

Figure 3

As mentionedabove, NO concentration in the first part of OCFFDR is more than the conventional FR. The proposed solution to minimize the amount of NO in this configuration is selective catalytic reduction of NO with NH3. The second reactor of OCFFDR is a catalytic fixed bed reactor with V2O5-WO3/TiO2catalysts. In this reactor, NO reacts with NH3 and O2 to produce N2 and H2O. Therefore, the content of NO leaving OCFFDR becomes negligible. So, this configuration can be considered as an environmentally friendly one. In the following, changes incomponents concentrations in this reactor have been discussed. Fig. 4(a) illustrates the reactants concentration profiles in the second reactor of OCFFDR. NH3 enters the second reactor in addition to the gas stream exiting the first reactor. All reactant concentrations decrease gradually until the NO concentration reaches 0.2 gmole.m-3 at the end of the reactor, which equals to 6 ppm. The concentration profile of the produced components in the second reactor, consisting water and nitrogen is shown in Fig. 4(b). Increasing trend for both components indicates good performance of the second reactor.

Figure 4

Fig. 5 describes concentration profiles for all components such as NO, N2, O2 and H2Oin both fluidized bed and fixed bed reactors of OCFFDR. As shown in Fig. 5(a), concentration of produced NO at the end of the first reactor increases to 58 ppm and then in the second reactor reaches to 6 ppm due reaction with NH3. O2 concentration profile is shown in Fig. 5(b). It


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increases noticeably at the beginning of the first reactor and then reduces slowly because of reacting with NH3 in the second reactor. Fig. 5(c) and (d) show the way N2 and H2O concentrations changes, respectively. Both N2 and H2O concentrations increase along the reactors. The rate of N2 production in the first reactor is more than its consumption rate. Furthermore, in the second reactor N2 production is the only source of this component. Although H2O is produced in both reactors, its production rate is greater in the fixed bed reactor as a product of three reactions.

Figure 5

Fig. 6depicts the effect of temperature as an important parameter on reaction rates.Fig. 6(a) shows the profile of temperature in FR and the first reactor of OCFFDR configuration. Initial temperature in the OCFFDR is higher than in FR (because of operating under optimum condition). A temperature peak at the first length of two reactors is a sign of exothermic reactions. Then, due to endothermic oxidation of N2 as well as decline in the rate of exothermic decomposition of AN, the temperature decreases in both diagrams. The outlet temperature in the first reactor of OCFFDR is 562 K which is equal to the inlet temperature of the second reactor. NH3 also enters the second reactor at this temperature (562 K). Temperature profile in the second reactor of OCFFDR is described in Fig. 6 (b). The peak at the entrance of the reactor is because of two exothermic reactions in SCR process. Decline in reaction rates along the reactor as well as presence of cooling water in the shell side of reactor results the temperature reduction equal to cooling water temperature of 573 K. Generally the favorable temperature for reduction reaction varies between 573 and 623 K

32

.

Therefore, the air enters the first reactor after preheating to 573 K. Fig. 6(c) shows how



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temperature changes along both reactors of OCFFDR. One temperature peak is observed in the zones close to the entrance of each reactor that occurs owing to high exothermic reactions.The first reactor (the fluidized bed reactor) works adiabatically so the temperature in this reactor is the adiabatic temperature. But the temperature of the fixed bed reactor (the second reactor) is not equal to adiabatic temperature. This reactor is cooled by cooling water in the shell side. Actually, if there was no cooling water in the second reactor, it worked adiabatically with higher average and peak temperature as shown in Fig. 6.

Figure 6

Fig. 7 illustrates the way that mole percents of all reactants and products changes in OCFFDR. All concentration distributions in OCFFDR also vary in similar way.

Figure7

The effect of bed temperature and gas velocity on ammonium nitrate concentration in fluidized bed of OCFFDR is depicted in Fig. 8 (a) and (b), respectively. High rate of ammonium nitrate decomposition leads to more reduction of ammonium nitrate concentration along the bed. In addition, as shown in Fig 8(a) and (b),ammonium nitrate concentration decreases with increasing the bed temperature and gas velocity. Therefore, in order to increase the conversion of ammonium nitrate, the bed temperature and gas velocity should be increased. In fluidized bed of OCFFDR, the conversion of ammonium nitrate is higher than FR owing to increasing ammonium nitrate decomposition rate with increasing the temperature. Heat and mass transfer as well as mixing degree can be greatly enhanced by increasing the gas velocity. Moreover, the


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obtained model confirms that a high fluidizing air velocity leads to formation of larger gas bubbles. As a result, gas interchange coefficient between the emulsion and bubble phases and also the residence time of gas bubbles inside the bed would be lower. Therefore, possibility of ammonium nitrate vapor transferring from the emulsion phase to the bubble phase is reduced and also the vapor of unconverted ammonium nitrate cannot leave the bubble phase.

Figure 8 In Fig 9, effect of the bed temperature and gas velocity on nitrogen oxide concentration in fluidized bed of OCFFDR is demonstrated. In spite of a considerable enhancement of ammonium nitrate conversion by increasing the bed temperature and gas velocity, concentration of NO, as an undesirable product, also increases along the fluidized bed reactor of OCFFDR. Figure 9 Model validation is carried out by comparison of modeling results of fluidized bed with experimental data presented by Bhowmicket al.20under design specifications and input data. By using the experimental conditions as the model inputs, ammonium nitrate conversion is estimated. Unfortunately, limited data are available for the experimental conditions. Results of comparison between the obtained model and experimental data are presented in Table 5. Moreover, the experimental data and model predictions for the bed temperature and the bed height, as process variables, are shown in Fig. 10(a) and (b), respectively. It can be observed that the conversions predicted by the model in OCFFDR are higher than those of experimental data. The estimated results are consistent with the pilot plant data as presented in Table 5 and Fig. 10.In the experimental data presented by Bohwmicket al., there is no report of nitrogen oxide concentration. Since the main goal of proposing novel configurations of OCFFDR is reduction of NOx emission, considerable enhancement is not observed for the ammonium nitrate conversion.



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 18 of 49

Figure 10 Table 5 6. Conclusion

In order to minimize the amounts of ammonium nitrate and NOx astwo environmental hazards, a novel configuration named OCFFDR is developed in this study.Ammonium nitrate decomposition takes place predominantly in the emulsion phase of fluidized bed. Liquid droplets are deposited on the hot surface of emulsion particles and then vaporized. Nitrogen, oxygen and water vapor are produced during decomposition of ammonium nitrate in the emulsion phase. On the other hand, NOx formation occurs via the oxidation of nitrogen. This novel configuration consists of a fluidized bed reactor followed by the fixed bed reactor in series. In the fluidized bed reactor, AN decomposes thermally into N2 and O2 with simultaneous NOx formation. Then in the fixed bed reactor, selective catalytic reduction of NOxwith NH3 occurs and finally O2, N2 and H2O leave the reactor. Accordingly, the amounts of AN andNOxare reduced as the main goals in this work. The performance of OCFFDR is investigated by considering a one-dimensional heterogeneous model. The operating conditions has been optimized via DE method to minimize both AN andNOx contents. . Since the experimental data are only presented for ammonium nitrate in literature, the results of modeling can be validated only with the data of conversionfor this component. Ammonium nitrate conversions obtained at various conditions are compared with the experimental results presented by Bhowmicket al. and a good agreement is observed between the model predictions and experimental measurements. Some parameters such as temperature, components concentrations profiles and gas velocity in both FR and OCFFDR are investigated. Results show that AN conversion in OCFFDR is approximately 2 times more than in FR. Furthermore, the amount of NOx leaving this configuration is one fifth the conventional


Page 19 of 49

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FR. This indicates a superiority of the proposed configuration comparing with other previous conventional ones. The other superiority of this novel configuration isthe air preheating which occursin the second reactor before entering the first reactor. This issue is economically efficient. Although, the optimum operating conditions as well as environmental advantages of this dual type configuration provides a deep insight into the performances of this novel configuration, experiments and cost evaluation should be supplemented to such a theoretical modeling for future plant design and evaluating the feasibilityof such a promising configuration in pilot plant scale. Supporting Information. The correlations for physical properties, mass and heat transfer coefficients are listed in Supporting Information (S1) as well as hydrodynamic properties in Supporting Information (S2). This information is available free of charge via the Internet at http://pubs.acs.org/.

Nomenclature:

Ac

[m2]

cross sectional area of each tube

ALR

[-]

air-to-liquid ratio

Ar

Archimedes number

ab

[m2]

interface area between bubbles and emulsion phase

CAN

[mol/m3]

concentration of ammonium nitrate

Cib

[mol/m3]

concentration of components in the bubble phase



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

Cie

[mol/m3]

concentration of components in the emulsion phase

cP

[J.mol-1.k-1]

specific heat of the gas at constant pressure

ct

[mol.m-3]

total concentration

D ij

[m2.s-1]

binary diffusion coefficient of component i in component j

Di m

[m2.s-1]

diffusion coefficient of component i in the mixture

DT

[mm]

Bed diameter

db

[m]

bubble diameter

dp

[m]

particle diameter

E

[J/mol]

activation energy

Hrxn

[J/mol]

heat of reaction

h

[W.m-2.K-1]

heat transfer coefficient

h

[m]

height of the reaction zone

K0

[1/s]

frequency factor

Kbe

[1/s]

gas interchange coefficient between the bubble and the emulsion phases

fi

[mol.s-1]

molar flow rate

Mi

[g.mol-1]

molecular weight of component i

Pr

[-]

Prandtl number

R

[J.mol-1.K-1]

universal gas constant

Re

[-]

Reynolds number

Remf

[-]

particle Reynolds number at minimum fluidizing conditions

rAN

[mol.m-3.s-1]


Page 20 of 49

Page 21 of 49

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


rbi

[mol.m-3. s-1]

reaction rate of component i in bubble phase

T

[K]

bulk gas phase temperature

u0

[m/s]

superficial gas velocity

ub

[m/s]

bubble rising velocity through a bed

umf

[m/s]

superficial gas velocity at minimum fluidizing conditions

ug

[m/s]

Gas velocity

yi

[mol.mol-1]

mole fraction of component i in the fluid phase

yie

[mol.mol-1]

mole fraction of component i in the emulsion phase

yib

[mol.mol-1]

mole fraction of component i in the bubble phase

z

[m]

height of the fluidized bed,

Greek letters

Symbol

Unit

Definition

Hf,i

[J.mol-1]

enthalpy of formation of componenti

H298

[J.mol ]

enthalpy of reaction at 298 K

δ

[-]

bubble phase fraction

mf

[-]

void fraction of bed at minimum fluidization

γ

[-]

volume fraction of catalyst occupied by solid particles in bubble phase



[kg.m-1.s-1]

)viscosity of fluid phase



[kg.m-3]

density of fluid phase

B

[kg.m-3]

density of catalytic bed

e

[kg.m-3]

Density of emulsion phase

p

[kg.m-3]

density of catalyst

-1



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 49

catalyst effectiveness factor

Superscripts andsubscripts

e

emulsion phase

b

bubble phase

References: [1]

Environment Agency, Attenuation of nitrate in the sub-surface environment, in: Science Report SC030155/SR2, 2005.

[2]

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[3]

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[4]

Suzuki, T.;Moribe, M.;Oyama, Y. ;Niinae, M. Mechanism of nitrate reduction by zerovalent iron: Equilibrium and kinetics studies, Chem. Eng. J.2012,183 271– 277.

[5]

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[6]

Lundberg, J.O. ;Weitzberg, E.; Cole, J.A.; Benjamin, N. Nitrate, bacteria and human


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[9]

Ho, C.M.; Tseng, S.K. ; Chang, Y.J. Autotrophic denitrification via a novel membraneattached biofilm reactor, Lett. Appl. Microbiol.2001, 33, 201–205.

[10] Ergas, S.J.;Reuss, A.F. Hydrogenotrophicdenitrification of drinking water using a hollow fiber membrane bioreactor, J. Water Supply: Res. Technol. Aqua.2001, 50, 161–171. [11] Mansell, B.O.; Schroeder, E.D. Hydrogenotrophicdenitrification in a microporous membrane bioreactor, Water Res.2002,36, 4683–4690. [12] Mo, H.;Oleszkiewicz, J.A.;Cicek, N.;Rezania, B. Incorporating membrane gas diffusion into a membrane bioreactor for hydrogenotrophicdenitrification of groundwater, Water Sci. Technol.2005, 51, 357–364 [13] Rezania, B.;Oleszkiewicz, J.A. ;Cicek, N. Hydrogen-dependent denitrification of water in an anaerobic submerged membrane bioreactor coupled with a novel hydrogen delivery system, Water Res. 2007, 41, 1074–1080. [14] Szekeres, S.; Kiss, I.;Bejerano, T.T.;Soares, M.I.M. Hydrogen-dependent denitrification in a two-reactor bio-electrochemical system, Water Res. 2001, 35, 715–719. [15] Chang, C.C.; Tseng, S.K.; Huang,H.K. Hydrogenotrophicdenitrification with immobilized Alcaligeneseutrophus for drinking water treatment, Bioresour. Technol.1999, 69, 53–58. [16] Kurt, M.; Dunn, I.J.; Bourne, J.R. Biological denitrification of drinking water using autotrophic organisms with H2 in a fluidized-bed biofilm reactor, Biotechnol.



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Page 24 of 49

Bioeng.1987, 29, 493–501. [17] Dries, D.;Liessens, J.;Verstraete, W.; Stevens, P.;Vost, P.; Ley, J. Nitrate removal from drinking water by means of hydrogenotrophicdenitrifiers in a polyurethane carrier reactor, Water Supply.1988, 6, 181–192. [18] Gros,

H.;Schnoor,

G.;

Rutten,

P.

Biological

denitrification

process

with

hydrogenoxidizing bacteria for drinking water treatment, Water Supply.1988,6, 193–198. [19] Vasiliadoua, I.A.;Karanasiosa, K.A.;Pavloubc, S.;Vayenas, D.V.

Experimental and

modelling study of drinking water hydrogenotrophicdenitrification in packed-bed reactors, J. Hazard. Mater.2009, 165,812–824. [20] Bhowmick, S.;Rao, H.;Sathiyamoorthy, D. Thermal denitration of ammonium nitrate solution in a fluidized-bed Reactor, Ind. Eng. Chem. Res.2010

1 8 94−84

[21] Rosser, W.A.;Inami, S.H. ; Wise, H. The kinetics of decomposition of liquid ammonium nitrate, Trans. Faraday Soc.1963, 67, 1753–1757. [22] Brower, K.R.; Oxley, J.C.;Tewari, M.

Evidence for homolytic decomposition of

ammonium nitrate at high temperature, J. Phys. Chem.1989, 93, 4029–4033. [23] Patil, D.G. ; Jain, S.R. ; Brill, T.B. Thermal decomposition of energetic materials 56. On the fast thermolysis mechanism of ammonium nitrate and its mixtures with magnesium and carbon, Propellants Explos. Pyrotech.1992, 17, 99–105. [24] Shah, M. S. ;Oza, T. M. The decomposition of ammonium nitrate, J. Chem. Soc.1932, 21,725. [25] Oommen, C.; Jain, S. R. Ammonium nitrate: A promising rocket propellant oxidizer. J. Hazard. Mater. A.1999

72

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[26] Gunawan, R.; Zhang, D. Thermal stability and kinetics of decomposition of ammonium


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nitrate in the presence of pyrite. J. Hazard. Mater.2009 16

7 1−7 8

[27] Sun, J. ; Sun, Z. ; Wang , Q. ; Ding , H.; Wang, T.; Jiang, Ch Catalytic effects of inorganic acids on the decomposition of ammonium nitrate, J. Hazard. Mater. B.2005, 127, 204–210. [28] Keenan, A. G.;Notz, K. ; Franco, N. B. Synergistic Catalysis of Ammonium Nitrate Decomposition, J. Am. Chem. Soc.1969,91,3168–3171. [29] Morinrga, K. ; Torikai, T.; Nakagawa, K.;Fujino, S.

b

α–alumina

powders by thermal decomposition of ammonium aluminum carbonate hydroxide (AACH),Acta mater. 2000, 48, 4735–4741. [30] Peng, L.; Zhang, J. Simulation of turbulent combustion and NO formation in a swirl combustor. Chem. Eng. Sci. 2009, 160, 2903 – 2914. [31] Zhiming, L.;Junhua , L.;Jiming , H. Selective catalytic reduction of NOx with propene over SnO2/Al2O3 catalyst, Chem. Eng. J.2010, 165, 420–425. [32] Roduit,R. ;Wokaun,A.;Baiker,A. global kinetic modeling of reactions occurring during selective catalytic reduction of NO by NH3 over Vanadia/Titania- based catalysts, Ind. Eng. Chem. Res.1998,37, 4577-4590. [33] Chae,H.J.;Choo,S.T.;

Choi,H.; Nam,I.S.; Yang,H.S. ; Song,S.L. direct use of kinetic

parameters for modeling and simulation of a selective catalytic reduction process, Ind. Eng. Chem. Res.2000,39 1159-1170. [34] Rangaiah,G.P.

Multi-objective optimization: techniques and applications in chemical

Engineering, first vol., World Scientific Publishing Co. National University of Singapore, 2008.



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Page 26 of 49

Differential evolutione a simple evolution strategy for fast

D D bb’ J 1997,78 22, 18-24.

[36] Babu,B.V. ;Angira,R. Modified differential evolutin (MDE) for optimization of non-linear chemical processes, Comput.Chem. Eng.2006,30, 989-1002. [37] Babu,B.V.;Sastry,K.K.N. Estimation of heat-transfer parameters in a trickle-bed reactor using differential evolution and orthogonal collocation, Comput.Chem. Eng.1999,23, 327- 339. [38] Price,K.;Storn,R.

Homepage of differential evolution as on April 25. URL:

http://www.ICSI.Berkeley.edu/storn/code.html, 2005. [39] Rahimpour,M.R. ;Khademi,M.H.;Bahmanpour,A.M. A comparison of conventional and optimized thermally coupled reactors for Fischer–Tropsch synthesis in GTL technology, Chem. Eng. Sci.2010, 65,6206-6214. [40]

Iranshahi,D.;Pourazadi,E.;Paymooni,K.;Rahimpour,M.R.

Utilizing DE optimization

approach to boost hydrogen and octane number in a novel radial-flow assisted membrane naphtha reactor, Chem. Eng. Sci.2012, 68, 236-249.

[41] Rahimpour,M.R.;Mirvakili,A.;Paymooni,K.

Differential evolution (DE) strategy for

optimization of hydrogen production and utilization in a thermally coupled membrane reactor for decalin dehydrogenation and Fischer-Tropsch synthesis in GTL technology, Int. J. Hydrogen Energy. 2011,36, 4917-4933.


Page 27 of 49

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Table 1.The kinetic parameters for fixed bed reactor over V2O5-WO3/TiO2 catalyst.

Kinetic parameters

Ea , NO (kcal / mol)

12.1

Ea , NH3 (kcal / mol)

57.6

H NH 3 (kcal / mol)

22.2

k0, NO

3.04  106

k0, NH 3

9.98  108

K 0, NH 3

69.1



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 28 of 49

Table 2.Input data used for numerical calculations in FR.

Parameter

values

Bed diameter (mm)

150

Bed temperature (K)

623

Mean sand size (μm)

300

Sand density (kg/m3)

2600

Fluidized bed height (mm)

300

Fluidizing air flow

2 Umf

Feed flow rate (L/h)

6

air-to-liquid ratio (ALR)

1.2

ammonium nitrate concentration in the feed solution (g/L)

150


Page 29 of 49

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


Table 3. Input data used for numerical calculations in OCFFDR. Fluidized bed reactor Parameter

values

Bed diameter (mm)

150

Bed temperature (K)

644

Mean sand size (μm)

300

Sand density (kg/m3)

2600


300

Fluidizing air flow

5Umf

Feed flow rate (L/h)

6

air-to-liquid ratio (ALR)

1.2

ammonium nitrate concentration in the feed solution (g/L)

150

Fixed bed reactor Inner diameter (mm)

100

Outer diameter (mm)

250

Fixed bed height (mm)

300

Bed temperature (K)

300

Average pore radius (nm)

12.4

Mean catalyst size (μm)

180

Total porosity (ε)

0.38



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 30 of 49

Table 4.The optimization results.

Parameter

range

Optimum value

Fluidized bed Temperature (K)

580-680

644

Gas velocity (ug/umf)

2-7

5

Fixed bed Temperature (K)

300-350

300


Page 31 of 49

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


Table 5.Model validation (For all runs, the following conditions were used: u/umf = 7, feed flow rate = 6 L/h, air-to-liquid ratio (mass flow rate of air/mass flow rate of solution) = 1.2, active zz

α = −45°) at an elevation of 500 mm (from the distributor), z

b

=

μ

20

runs parameters

1

2

3

4

Feed concentration (g/l)

150

150

150

75


800

700

600

800

Reaction zone length (mm)

300

200

100

300

The ratio of height to diameter of the bed

2

1.3

0.67

2

Bed temperature (K)

598

623

623

623

50

35

55

53

39

57.3

6

11.5

4.18

Conversion of ammonium nitrate from the 46 experimental data (%) Conversion of ammonium (%) from the 47.5 model predictions Error (%)

3.2



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Page 32 of 49

List of figures: Fig. 1: A schematic diagram of configuration of (a) FR (b) OCFFDR.

Fig. 2: The concentration of (a)ammonium nitrate(b) nitrogen oxide (c) nitrogen (d) oxygen (e) water along fluidized bed of OCFFDR and FR.

Fig.3: The conversion of ammonium nitrate and mole percent of NO (a) FR (b) OCFFDR.

Fig.4: The concentration profiles of (a)reactants (b) products in the second reactor of OCFFDR. Fig. 5: The concentration profiles for (a) NO(b) N2(c) O2(d) H2Oin both fluidized bed and fixed bed reactors of OCFFDR.

Fig. 6: A comparison between (a) temperature profile in FR and first reactor of OCFFDR configuration(b) temperature profile in fixed bed of OCFFDR (c) temperature profiles in OCFFDR.

Fig 7: Mole percents of all reactants and products of OCFFDR.

Fig. 8: The effect of (a)bedtemperature and (b) gas velocity on ammonium nitrate concentration in OCFFDR.

Fig. 9: The effect of (a)bedtemperature and (b) gas velocity on nitrogen oxide concentration in OCFFDR.

Fig. 10: Model validation: ammonium nitrate conversions versus (a) bed temperature (b) the height of bed.


Page 33 of 49

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NO O2 N2 H 2O NH4NO3

Sand

Ammonium nitrate + air

Figure 1(a)



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Page 34 of 49

NH3

NO O2 N2 H 2O

Air

Sand N2 O2 H 2O Ammonium nitrate + air Fixed bed rector

Fluidized bed reactor

Figure 1(b)


Page 35 of 49

Concentration of AN (gmol/m3)

3.5 FR OCFFDR

3 2.5 2 1.5 1 0.5 0

0

0.5 1 1.5 Dimensionless height (h/Dt)

2

Figure 2 (a)

2 FR OCFFDR

3

Concentration of NO (gmol/m )

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


1.5

1

0.5

0

0


Figure 2(b)


2

Page 36 of 49

9 8 FR OCFFDR

7 6 5 4 3

0


2

Figure 2(c)

1.4 3

Concentration of Oxygen (gmol/m )

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

Concentration of Nitrogen (gmol/m3)


1.3 FR OCFFDR

1.2

1.1

1

0.9

0

0.5 1 1.5 Dimensionless height (h/Dt) Figure 2 (d)


2

Page 37 of 49

3

Concentration of Water (gmol/m )

0.02

FR OCFFDR

0.015

0.01

0.005

0

0


2

Figure 2 (e) 0.5

10

FR 0.4

8

0.3

6

0.2

4

0.1

2

0

0

0.5

1

1.5

Dimensionless height (h/Dt) Figure 3 (a)


0 2

NOx mole percent

Ammonium Nitrate Conversion

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



20

1

0.5

0

10

0

0.5

1

1.5

Dimensionless height (h/Dt) Figure 3(b)


0 2

NOx mole percent

OCFFDR Ammonium Nitrate Conversion

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 38 of 49

2.5 NO NH3

2

O2

1.5

1

0.5

0

0


2

Figure 4(a) Concentration of produced components (gmol/m3)

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


Concentration of consumed components (gmol/m3)

Page 39 of 49

20 N

2

H O 2

15

10

5

0

0

0.5 1 1.5 Dimensionless height (h/Dt) Figure 4(b)


2


3

Concentration of NOx (gmol/m )

2

1.5

1

0.5 Fluidized bed reactor Fixed bed reactor 0

0

1 2 3 Dimensionless height (h/Dt)

4

Figure 5 (a)

1.4 3

Concentration of Oxygen (gmol/m )

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 40 of 49

1.2 1 0.8 Fluidized bed reactor

Fixed bed reactor

0.6 0.4 0.2 0

0

1 2 3 Dimensionless height (h/Dt) Figure 5 (b)


4

Page 41 of 49

14 12

2

3 Concentration of N (gmol/m )

16

10 8 6 4 Fluidized bed reactor 2

0

Fixed bed reactor


4

Figure 5 (c)

2.5 Fluidized bed reactor

2

3

Concentration of H O (gmol/m )

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


Fixed bed reactor

2

1.5

1

0.5

0

0

1 2 3 Dimensionless height (h/Dt) Figure 5(d)


4


700 FR OCFFDR 650 Temparature (K)

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 42 of 49

600

550

500

0


Figure 6(a)


2

Page 43 of 49

640 Fixed bed temperature (K)

630 620 610 600 590 580 570 560

coolant temparature 2


4

Figure 6 (b)

700 Fluidized bed reactor

Fixed bed reactor

680 Temparature (K)

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


660 Adiabatic temperature

640 620 600 580 560

0

1 2 3 Dimensionless height (h/Dt) Figure 6 (c)


4


Fluidized bed reactor 80 Mole percents (%) in OCFFDR

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 44 of 49

Fixed bed reactor

N2

70 60

NH3

20

50

15

40

10 NH4NO3

30

5 1.6 1.8

O2

20

2

NO

2.2 2.4

H2O

10 0

0


Figure 7


4

3.5 3 2.5 2 1.5 1 0.5 0 0 0.1 0.2 0.3

620

630

Length (m)

640

660

650

670

Bed temperature (K)

Figure8(a)

Ammonium nitrate concentration (gmol/m 3)

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


Ammonium nitrate concentration (gmol/m 3)

Page 45 of 49

4

3

2

1

0

0 0.1

5 4

0.2

3 0.3

Length (m)

2

ug/umf



Figure8(b)

1.5 NO concentration (gmol/m3)

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 46 of 49

1

0.5

0 700 0.99

650

0.66

600 Bed temparature (K)

0.33 550

0

Length (m)

Figure9 (a)


4 3 2 1

0.3

0 5

0.2 0.1

4 3 2

ug/Umf

Length (m)

0

Figure9(b)

80 Conversion of ammonium nitrate (%)

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


NO concentration (gmol/m3

Page 47 of 49

Experimental Model (Bhowmick) Model

70

60

50

40

30 560

580

600

620

Operating bed temperature (K)


640

660


Figure10 (a)

60 Conversion of ammonium nitrate (%)

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 48 of 49

50 40 30 20 Model Experimental Model (Bhowmick et al.)

10 0

0

0.5

1

1.5

Dimensionless height (h/Dt)

Figure10 (b)


2

2.5

An Environmentally Friendly Configuration for Ammonium Nitrate

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