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E-Beam SO2 and NOx removal from flue gases in the presence

of fine water droplets

Ioan Calinescu a, Diana Martin b, Andrezj Chmielewski c, Daniel Ighigeanu b,n

a University POLITEHNICA of Bucharest, ]149 Calea Victoriei St., 010072 Bucharest, Romaniab National Institute for Lasers, Plasma and Radiation Physics, Electron Accelerators Laboratory, P.O.Box: MG-36, ]409 Atomistilor St., 077125 Magurele, Ilfov, Romaniac Institute of Nuclear Chemistry and Technology, ]16 Dorodna St., 03-195 Warsaw, Poland

H I G H L I G H T S

c The medium-energy EB accelerators are proposed for flue gases treatment.

cThe energy losses in the windows and in the air gap between them are reduced.

cTo increase the density of the reaction medium and to reduce the penetration depth of EB fine water droplets (FWD) are used.

cDetermining the energy efficiency the favorable effect of the method was demonstrated.

cThe maximum amount of FWD was determined from the total energy balance of the process.

a r t i c l e i n f o

Article history:

Received 30 May 2012

Accepted 11 October 2012Available online 20 November 2012

Keywords:

Flue gasesNOx and SO2 removal

Electron beam

Fine water droplets

a b s t r a c t

The Electron Beam Flue Gas Treatment (EBFGT) has been proposed as an efficient method for removal of

SO2and NOx many years ago. However, the industrial application of this procedure is limited to just a

few installations. This article analyses the possibility of using medium-power EB accelerators for off-

gases purification. By increasing electron energy from 0.7 MeV to 12 MeV it is possible to reduce the

energy losses in the windows and in the air gap between them (transformer accelerators can be applied

as well in the process). In order to use these mid-energy accelerators it is necessary to reduce theirpenetration depth through gas and this can be achieved by increasing the density of the reaction

medium by means of dispersing a sufficient amount of fine water droplets (FWD). The presence of FWD

has a favorable effect on the overall process by increasing the level of liquid phase reactions. A special

reactor was designed and built to test the effect of FWD on the treatment of flue gases with a high

concentration of SO2and NOx using high-energy EBs (9 MeV). By determining the energy efficiency of

the process the favorable effect of using FWD and high-energy EB was demonstrated.

& 2012 Elsevier Ltd. All rights reserved.

1. Introduction

New technologies and processes have promoted our economic

growth and have been remarkably changing our lifestyles. How-ever, technological innovation is not always welcome. It has

impact on the environment and may have effects related to the

peoples health. The emission of inorganic pollutants such as

nitrogen oxides (NOx) and sulfur dioxide (SO2) has been remark-

ably reduced by application of state-of-the-art technologies

during the past 60 years. However, industrialized countries have

been using the big amounts of oil and coal for energy production

via combustion of fossil fuels to convert chemical energy of the

substrate into electricity, vehicles fuels and process heat to be

used in industries.

Although the developing countries also try to increase theconsumption of environment-friendly energies instead of fossil

fuels, the steep demand for energy due to the recent economic

growth makes it difficult or even impossible to reduce the usage

of fossil fuels. This causes a large amount of emission of NOx, SO2,

as well as carbon dioxide to the atmosphere (Gaffney et al., 1987;

Kato and Akimoto, 2007;Ramanathan and Feng, 2009;Streets and

Waldhoff, 2000).

While the industrial countries have achieved a sufficient

reduction of NOx and SO2 emissions, it is still an urgent issue

for the developing countries to follow this trend. To meet the

strict regulations established by local governments, the wet lime

scrubber method and the selective catalytic reduction method

Contents lists available at SciVerse ScienceDirect

journal homepage: w ww.elsevier.com/locate/radphyschem

Radiation Physics and Chemistry

0969-806X/$- see front matter& 2012 Elsevier Ltd. All rights reserved.

http://dx.doi.org/10.1016/j.radphyschem.2012.10.008

n Corresponding author. Tel.: 40 214574346; fax: 40 214574243.

E-mail addresses: [email protected] (I. Calinescu),

[email protected] (A. Chmielewski),

[email protected] (D. Ighigeanu).

Radiation Physics and Chemistry 85 (2013) 130138
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have been applied to treat SO2 and NOx. However, the wet lime

scrubber method requires wastewater treatment, and the cata-

lysts have to be replaced periodically. New technology is expected

for simple and simultaneous treatment processing of the both

pollutants. The electron-beam irradiation process for flue gas

purification (EBFGT) has been proposed as an efficient method

because it has the following advantages (Hatano et al., 2011):

has simultaneous denitrification and desulfurization possibilities, no wastewater treatment is required, no expensive catalyst is required, provides simple process and its operation, produces profitable products.

The application of electron beams to treat flue gases, such as

removing sulfur dioxide, was started by Ebara Corporation in

Japan and in the US (Chmielewski, 2011).

There are only few pilot and industrial installations for flue

gases treatment by electron beam (EB) irradiation (Chmielewski

et al., 2004) operated at this moment. Its drawback, like in other

conventional technologies, is high energy consumption (the

necessary power for the electron beam is around 24% from the

total electrical energy produced by the plant) (Hackman andAkiyama, 2000;Licki et al., 2003) and the difficulties in operation

of very high power accelerators. That is why it is mandatory to

find new solutions and to develop strategies for diminishing

radiation dose absorbed in the flue gas and to optimize the

process for better uses of EB energy.

Subjected to the electron beam irradiation process, the main

components of flue gases (N2, O2 and H2O), are transformed into

divergent ions and radicals. The primary species include: e , N2 ,

N , O2 , O , H2O

, OH , CO2 , CO , N2

n, O2n, N, O, H, OH and CO

(Matzing and Paur, 1992;Tokunaga and Suzuki, 1988). In the case

of high water concentration, oxidizing radicals HO and HO2 and

excited species such as O(3P) are the most important product

formed (Person and Ham, 1988). In the presence of water

droplets, the radiolytically produced hydrated electron reactsvery fast with the dissolved oxygen to produce the superoxide

(O2) radical. Since the O2

has a pKa value of 4.7, it will be

converted to HO2in acidic medium. HO2 is also produced by the

reaction of H-atom with oxygen. However the yield from this

reaction is only about 0.06 mmol per joule.

N2,O2,H2O vapors_at_high_concn e-HO,HO2

,On,ions,excited-species

1

In the presence of these reactive species, NOx and SO2 from

flue gases are oxidized and produce nitric acid and sulfuric acid,

respectively, as intermediate products. These acids are neutra-

lized with ammonia, giving powders of ammonium nitrate and

ammonium sulfate, respectively (Namba et al., 1998) (Fig. 1).

The total yield of SO2 removal consists of the yield of thermaland radiation induced reactions that can be written (Chmielewski

et al., 1995a;Matzing et al., 1993):

ZSO2 Z1 F,T Z2 D,aNH3,T

2

The yield of the thermal reaction depends on the temperature

and humidity. The yield of the radiation induced reaction depends

on the dose, temperature and ammonia stoichiometry. The main

parameter in NOxremoval is the dose.

The presence of water vapors is mandatory for the efficient

removal of SO2and NOxfrom gases. By radiolysis of water the HO

radical is obtained and this radical will oxidize both SO2and NOx(Genuario, 2009):

NOHO

M-HNO2M (3)

NO2HOM-HNO3M (4)

SO2HOM-HSO3M (5)

HSO3O2-SO3HO2 (6)

SO3H2O-H2SO4 (7)

NOHO2-NO2HO

(8)

A gas humidity 810 vol% is necessary to obtain the optimal

removal-efficiencies of both pollutants (Chmielewski, 2007).

The selection of an adequate accelerator is an important issue

in the process engineering. The primary effect of any ionizing

radiation is based on its ability to excite and ionize molecules, and

this leads to the formation of free radicals, which then initiate

chemical reactions.

Accelerated electron beams suitable for flue gas treatment

have sufficient energy (up to 5 MeV) to affect the electrons in the

atom shell, but not its nucleus, and can therefore only initiate

chemical reactions (Zimek, 1995). Typically, the reactions

initiated by electron beam are extremely fast and are completed

in fractions of a second.

Electrons that are capable of electronically exciting and ioniz-

ing molecules, such as N2, O2, CO2, H2O etc., must have energies in

the range from 12 to 16 eV. Such electrons can be produced from

fast electrons by the energy degradation process in solids, liquids,

and gases. These secondary electrons show energy distribution

with the maximum in the range from 50 to 100 eV. In contrast tofast electrons, exhibiting energies in the keV and MeV range,

secondary electrons are capable of penetrating solids and liquids

only a few nanometers. Consequently, they generate ions, radi-

cals, and excited molecules in droplets along the paths of the

fast electrons (Drobny, 2010).Fig. 2 illustrates schematically the

process of generation of reactive species.

The basic fundamental properties for the EB machine; beam

current and beam energy should be derived from the process

requirements to ensure satisfactory results with minimum capital

and operating costs. The power of EB is determined function of

the flow rate of the treated material and the absorbed dose

needed for the process:

Dave FpP= M=T

9

Fig. 1. The main reactions used in EBFGT to convert SO2and NOX(Namba et al., 1998).

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whereD(ave)is the average absorbed dose in kGy, Pis the emitted

radiation power in kW, Tis the treatment time in s and Mis the

mass of irradiated material in kg.

The factorF(p)is the fraction of emitted power absorbed by the

material, which depends on the size, shape, thickness and density

of the object and the penetrating quality of the radiation. The

energy absorption in the primary and secondary window shouldbe considered in the case of EBFGT. This quantity is difficult to

measure (by using dosimeters placed inside the reaction vessel),

but it can be calculated by Monte Carlo simulation. It can range

from 0.25 to 0.75, depending on the particular application.

EB energy losses in the beam windows and in the air space

between them are high for the low energyhigh power accel-

erators that are presently used for air pollutants removal

(Chmielewski et al., 1995b). The total EB energy losses (back-

scattering, beam windows and air gap) are substantially lower

with higher EB incident energy (seeFig. 3). The useful EB energy

from input energy is around 50% for 0.5 MeV and about 95% above

3 MeV. The lower electrical efficiencies of accelerators with

higher energies are partially compensated by the lower electron

energy losses in the beam windows. In addition, accelerators with

higher electron energies can provide higher beam powers with

lower beam currents (Cleland, 2007).

Much attention should be paid to the range of the electron beam

penetration. The penetration of high-energy (relativistic) electron

beams in irradiated materials increases linearly with the incident

energy. The electron pathway range also depends on the atomic

composition of the irradiated material. The energy deposition is

caused mainly by collisions of the incident electrons with atomic

electrons. Therefore, materials with higher electron contents (elec-trons per unit mass) will absorb higher doses near the entrance

surface, but shorter electron penetration ranges (Cleland, 2005).

Fig. 4 shows the depthdose distribution curves for beam

energies between 1.0 and 5.0 MeV in centimeters of water as

derived from Monte Carlo calculations using the ITS3 (Integrated

Tiger Series code) (Cleland, 2004).

For mid-energy (500 keV to 5 MeV) and high-energy (5 MeV to

10 MeV) electron accelerators, it is common to express beam

penetration on the basis of equal-entrance and exit doses in unit

density material. InFig. 5 are presented the calculated values of

penetration depth (on the basis of practical range R(p) for flue

gases and for flue gases with fine water droplets (FWD), the

volume fraction of water is designated as L (Vaq/Vgas), whereVaqand V

gas refer to the irradiated volumes for the two phases,

L4 103.

The range parameters can be correlated with the incident

electron energy E with sufficient accuracy for industrial applica-

tions by using the following linear equations (for polyethylene)

(Cleland, 2005):

Rp 0:510E0:145 10

Electron ranges in other materials can be estimated by multi-

plying the polyethylene range with the ratio of their CSDA ranges.

Rmaterial Rpolyethylene CSDAm=CSDApe 11

CSDAranges for many materials with a wide range of electron

energies can be obtained from ICRU Report 37 or from (http://

www.nist.gov/pml/data/star/index.cfm).Supposing exhaust gases at a temperature of 60 1C (density

r1.06 103 g/cm3) are treated by an electron accelerators

equipped with a Ti foil (50 mm, r4.5 g/cm3) window, air gap

15 cm and another Ti foil for the reactor (50 mm), the range of

electrons generated from 750 and 2500 kV are 235 and 1240 cm,

respectively (seeFig. 5). The depth of the reactor in the irradiation

direction must be less than these values to avoid non-irradiation

space in the reactor.

Fig. 2. The process of generation of reactive species by high energy electrons.

Fig. 3. Electron energy losses function of incident electron energy for flue gases

treatment by EB (Cleland, 2007).

Fig. 4. Electron energy deposition vs. thickness density in water at 1.0, 1.5, 2.0,

2.5, 3.0, 3.5 4.0, 4.5 and 5.0 MeV incident electron energy (IAEA, 2010).

I. Calinescu et al. / Radiation Physics and Chemistry 85 (2013) 130138132
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Although the medium-energy EB (2.5 MeV) are used with high

efficiency (with lower total energy losses, seeFig. 3), the penetra-

tion depth of these EB is too high (approx. 12.4 m, see Fig. 5). In

order to reduce the penetration depth, it is necessary to increase

the density of the medium. This can be achieved by dispersing

FWD in flue gases. The influence of volume fraction of water (L) in

flue gases on the density of the gas medium and on the penetra-

tion depth of EB with 2.5 MeV is presented inFig. 6.

Several reasons showing the potential importance of droplet-phase oxidation in the EBFGT process can be outlines (Cooper

et al., 1998):

High driving force for the most oxidation process due to lowGibbs free energy of the products obtained in liquid phase;

High solubility of the mixture components (SO2 and theintermediates NO2, N2O4) resulting in an increase in its

liquid-phase concentrations;

Rapid rates of the aqueous-phase oxidation process initiatedby ionizing radiation.

Regarding the primary partitioning of the dose rates between

the irradiated phases, denotedDRgasand DRaq, one notes (Cooper

et al., 1998) that its magnitude is governed mainly by the ratio of

the phases densities, rgasand raq.Since the ratio raq/rgasis typically

Z103, then DRaq/DRgasraq/rgasZ103, assuming that the stopping

powers of the gas and liquid phase are quite the same. Thus the dose

rate in the droplet is higher than that of the gas by a factor of at least

three orders of magnitude. This means that the ratio of the chemical

reactions rates of the pollutants oxidation in the two phase system

is controlled by the phases densities.

With regard to the portioning of absorbed doses between the two

phases, which determines the extent of pollutant removal duringirradiation, one gets (Cooper et al., 1998):Daq/DgasZraq*L/rgas.

WhenL is quite low (in a typical EBFGT process Lr106), it is

unlikely that the radiation-induced reactions in the liquid phase

can a play a significant role in the removal of pollutants from the

irradiated gas, but ifL 103 the reactions in liquid phase become

important. For such conditions, the chain oxidation takes place in

liquid phase, but the chain is initiated by active particles formed

in the gas and liquid phase (Potapkin et al., 1995).

It was found (Yermakov et al., 1995) that the extents of NOxand

SO2 depletion on simultaneous irradiation and spraying of water

(or water solution) are sensitive not only to absorbed dose but also

to the amount of water existing in the gas as liquid droplets.

The conversion of SO2 can be obtained by reactions in gas

phase (thermal and radio-induced) and by reactions in liquid

phase. Because of high value of solubility of SO2in water (Henrys

constant1.23 Mnatm1) SO2 is easily absorbed in water and

here the SO2 is oxidized by a chain reaction in the presence of

dissolved oxygen (Potapkin et al., 1995). The conversion of NO

takes place only by radio-induced reactions. In gas phase NO is

oxidized to NO2by reactions of NO with O and O3. In the absence

of water droplets the removal efficiency of NO dropped sharply

after NO conversion to NO2(Potapkin et al., 1995). This is because

of the influence of the reactions with N and NH2(Matzing, 1989):

NO2 N-2NO 12

NO2 N-N2OO 13

NO2 NH2-N2O H2O 14

In the presence of fine water droplets the quenching of NO2take

place by dissolution and reaction in droplets of water (the Henrys

constant of NO2 is 6 times higher than the value for NO:

1.23n102 Mnatm1 respectively 0.195n102 Mnatm1 (Squadrito

and Postlethwait, 2009).

The dissolved NO2can be oxidized by OH radicals obtained by

water radiolysis or reduced by reaction with S(IV) compounds

(Potapkin et al., 1995):

NO2 OH-HNO3 15

No2 HSO3-NO

2 HSO

3 16

No2 HSO3 H

-

H2OSO24 NH

4 17

NO2 HSO3--HSO

4 N2 18

However, the experiments of Yermakov were done at quite

low value ofL (about 104), at such values the influence of FWD

on density of the gas-liquid system is quite low and is not

possible to use the accelerators with mid-energy (about 2 MeV)

due to high penetration depth of electrons (seeFig. 5).

Our purpose is to treat flue gases at high values of L (about

103). At this level it is possible to achieve a significant increase

in the density of the medium (45 times higher than the density

of flue gases without FWD) and also it is possible to use electron

beam with mid-energy in irradiation reactors with a small

diameter. Moreover, the radiation-induced reactions developed

in liquid phase will play a significant role and will increase the

overall efficiency of the process.

Fig. 5. The penetration depth of electron beam function of electron energy in flue

gases (r1 g/L) and in flue gases with FWD (L 4n103, r5 g/L).

Fig. 6. The influence of liquid water fraction (L) in flue gases on the density of flue

gases with FWD and penetration depth for EB of 2.5 MeV.


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that are mechanically fitted with screw clamps and helically and

equidistant distributed to 1201. The high pressure causes water to be

sprayed through nozzles as small droplets of the diameter close to

10 mm.

The electrons are introduced in the EB reactor through two exit

windows, one of each in the form of cylinder, made of 100 mm-

thick aluminum foils. The EB current is collected on the electrical

insulated inner vessel of the EB reactor, integrated and displayed

on the control desk.

The characteristics of ALIN-10 EB accelerator used in our

experiments (Ibeam current, Eelectrons energy and PEB

power) highlight onFig. 8, are

Iexit accelerator1371 mA

Eexit accelerator9.170.23/0.1 MeV

ireactor as Faraday cup (without FWD): 1011 mA

Ireactor as Faraday cup (with FWD): 0.51 mA

Pexit accelerator13 mA 9.17 MeV119.21 W

Preactor inside power(without FWD) 10 (11) mA 9.17 MeV91.7

(100.87) W (about 27.317.34 W are losses in the two

windows of the reactor, the two air gaps, and other uncon-

trolled losses).

3. Results and discussion

In our experiments, fine water droplets, that are produced

with a high pressure pump, are injected simultaneously with a

high energy (69 MeV) EB into a proper modified EB reactor

reported in our previous paper (Ighigeanu et al., 2012) for the

following purposes:

To promote the use of medium to high-energy EB accelerators

for air pollutants removal in order to be in accordance withCleland recommendations: the electron energy losses in the

dual beam windows and the air space will be substantially

lower with higher electron energies (Cleland, 2007).

To reduce the length of useful penetration of high energyelectrons that is in air much bigger than the length of the usual

EB reactors (EBRs) that are presently used for air pollutants

removal. Therefore, the presence of FWD simultaneously with

a high energy electron beam makes possible the use of EB

reactors with suitable size.

In view of above conditions, the injection of FWD in conjunction

with high energy EB in the gaseous mixture is able to shorten EB

ranges and to improve high energy EB absorption and consumption

in useful chemical reactions. A laboratory accelerator of high

energy (69 MeV) was used to reveal the effect of fine water

droplets. Research must be pursued using mid-energy accelerators

(12 MeV).

As evaluation criterion of the process were calculated pollu-

tant (P) removal efficiency (RE), reactor energy density (RIED), and

energy efficiency (EE) by using the following expressions

(Zhu et al., 2009):

RE % PinletPoutlet

Pinlet 100% 19

RIED kJ=L

EB_input_powerW

gas_f low_rate L=min 60 103 20

EE g=kWh

Pinlet RE

RIED 103 21

where [P]inletis in mg/N m3.

A number of experiments were conducted using flue gases

flow rates ranging between 5.2 and 14.0 m3/h. Two operation

modes were tested EB only or EB combined with FWD. The

treatment conditions and the results are shown in Table 1. For

comparison, the results obtained previously on the same installa-

tion but without FWD, are presented.

It can be noticed that the presence of FWD causes an increase

of the pollutants removal efficiency. This observed effect is bigger

in the conditions when the values of the removal efficiency in the

absence of FWD are lower, i.e. lower doses regions.

For different reaction conditions the density of reaction mix-

ture will be changed and from this reason also penetration depth

and the EB power effectively used.Table 2presents the treatment

conditions, the effectively used EB power (determined according

to the accelerator power, the losses in windows and the air gap,

and function of the ratio between the reactor length and thepenetration depth) and also the results obtained: reactor energy

density and energy efficiency determined for effectively used EB

power and for total EB power.

From the values presented inTable 2it can be noticed that the

presence of FWD leads to an increase in the density of the

medium and thus, the penetration depth of EB in the reaction

medium is significantly changed. Because the reactor length is

limited to 300 cm, we can consider that the ratio between the

reactor length and the penetration depth provides information

about the effectively used power. From this value of power used

we can determine the real values of RIED and EE.

From the analysis of values listed inTable 2we can notice that

in the presence of FWD the real EE values are lower than those

obtained in the absence of water droplets. However, this is

Table 1

Treatment conditions and results obtained for flue gas treatment by EB, in the presence of ammonia and of FWD.

No. Treatment conditions Results Obs.

Flow rate (l/h) NH3 stoecha Initial conc. (ppmv) Treatment type RE SO2 RE NOx

Gases Liq. water SO2 NO

1 1000 0 0.8 2000 400 EB 0.98 0.62 Ighigeanu et al. (2012)

2 5200 0 0.9 812 44 EB 0.85 0.783 5200 50 0.9 812 44 EB FWD 0.94 0.98

4 14,000 0 0.6 1116 102 EB 0.70 0.36

5 14,000 50 0.6 1116 102 EB FWD 0.88 0.88

6 14,000 0 0.95 423 135 EB 0.97 0.32

7 14,000 50 0.95 423 135 EB FWD 0.98 0.84

8 14,000 0 0.95 520 292 EB 0.97 0.20

9 14,000 50 0.95 520 292 EB FWD 0.98 0.8

a NH3 stoech. [NH3]/(2 [SO2] [NOx]), with all concentrations in ppmv.


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compensated by the low level of EB power used in the absence

of FWD.

From the analysis of the energy efficiency values function of

the EB power provided by the accelerator the positive effect of

FWD presence in the reaction mixture can be noticed. This effect

is more important for NOx. In order to compare our experimental

data with those obtained in an industrial installation, we made

some calculations for the operational conditions of EBFGT plant in

EPS Pomorzany, Poland (Chmielewski et al., 2004). The values are

presented inTable 3.

Our experiments 8 and 9 are carried out with pollutants

concentrations similar with those existing in the Pomorzany power

plant. It can be noticed that the values obtained for the energy

efficiency (EE) are higher when FWD are used as compared to those

obtained in the industrial plant (for effectively used EB power).

It is also important to determine the power of the pump used

to obtain FWD. The output power of this pump can be determined

by the equation (Perry, 1999):

P H*Q=3:599*10

6

22

Table 2

RIED and EE values for different treatment conditions.

No T reatment condi ti ons Results for effectively used EB power Results for total EB power (96.3 W)

Liquid water

fraction,L

Density (g/L) Penetration

depth, (cm)

Absorbed EB

power (W)

RIED (kJ/L) EE (g/kWh) RIED (kJ/L) EE (g/kWh)

SO2 NOx SO2 NOx

1 0 1.06 4530 9 0.032 172.8 10.3 0.347 16.2 1.0

2 0 1.06 4530 9 0.006 316.5 7.4 0.067 29.6 0.73 0.0096 10.64 426 82.6 0.057 38.1 1.0 0.067 32.7 0.9

4 0 1.06 4530 9 0.002 964.4 21.3 0.025 90.1 2.0

5 0.0036 4.6 1260 25 0.006 436.5 18.7 0.025 113.3 4.9

6 0 1.06 4530 9 0.002 506.6 25.0 0.025 47.3 2.3

7 0.0036 4.6 1260 25 0.006 184.2 23.6 0.025 47.8 6.1

8 0 1.06 4530 9 0.002 622.7 33.8 0.025 58.2 3.2

9 0.0036 4.6 1260 25 0.006 226.5 48.7 0.025 58.8 12.6

Table 3

Values for industrial EBFGT plant of Pomorzany (Chmielewski et al., 2004).

Results for total EB power Results for effectively used EB power ( 21.8% losses)

SO2 NOx SO2 NOx

Flow rate for one EB accelerator, (N m3/min) 1,125,000 1,125,000 1,125,000 1,125,000

EB power (kW) 259,700 259,700 203,085 203,085

RE (%) 0.9 0.7 0.9 0.7

Pollutant inlet (mg/N m3) 1500 391 1500 391

RIED (kJ/L) 0.014 0.014 0.011 0.011

EE (g/kWh) 97.47 19.76 123.31 25.00

Table 4

Values of beam power losses function of EB energy obtained at pilot plant operated at EPS Kaweczyn (for 0.5, 0.6 and 0.7 MeV) and calculated for different energies of

electron beam in the presence of FWD (for 12 MeV).

EB energy

(MeV)

Beam power losses

(windowsair)

(kW or %)

Losses due to vessel diameter

(1.6 m)

Volume ratio

liquid:gas,L

Power used to obtain

FWD(P) (kW)

Proper diameter

to avoid losses, m

Energy economy

(kW or %)

Without FWD

(L1) (kW or %)

With FWD

(L2) (kW or %)

EnEc1 EnEc2

With out

FWD

With FWD (L1 (L2P))

0.5 47.4 0.4

0.6 29.2 2.9

0.7 21.8 14.8

0.7 21.8 14.8 5.2 0.0001 3.9 2.1 1.8 5.70

1 14.3 46

39 0.0001 3.89 3.81 3.47 3.00 10.5

19 0.0005 19.45 3.81 2.54 8.04 15.54

4 0.001 38.90 3.81 1.91 3.08 10.58

1.5 8.4 74

56 0.0005 19.45 6.71 4.47 1.83 11.57

39 0.001 38.90 6.71 3.35 4.21 9.19

25 0.0015 58.35 6.71 2.68 9.09 4.31

10 0.002 77.80 6.71 2.24 13.71 0.31

1 0.003 116.70 6.71 1.68 43.56 30.16

2 6.2 82

74 0.0005 19.45 9.56 6.37 11.52 4.08

65 0.001 38.90 9.56 4.97 21.83 6.23

53 0.0015 58.35 9.56 3.98 29.90 14.3

39 0.002 77.80 9.56 3.32 35.21 19.61

19 0.003 116.70 9.56 2.49 53.77 38.17


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where P is the output power of the pump (kW), H is the total

dynamic head (Pa) and Qis the capacity (m3/h).

Table 4 contains some data reported from the EBFGT pilot

plant experiments at EPS Kaweczyn, Poland (20,000 N m3/h,

100 kW beam power and initial electrons energy of 0.7 MeV)

(Chmielewski et al., 1995a) and calculated values of EB losses for

different energies of electron beam in the presence of FWD (for

1 to 2 MeV).

It can be noticed how the losses in windows and air gap aredecreasing while the electrons energy raises but the reactor

diameter has to be very large in order to trap the full energy of

electrons. The losses due to the reactor diameter are lower in the

presence of FWD. In determining the power necessary to obtain

FWD it can be seen that there is a limitation in the amount of

liquid water used.

Thus using EB of 1 MeV in a reactor with 1.6 m diameter in the

absence of FWD the power losses are 46% which means 46 kW for

the pilot plant that has 2 EB accelerators of 50 kW. In the presence

of FWD the losses are reduced at 39%, 19% or 4% (function of

Liquid:gas ratio used) for obtaining FWD a power of 3.938.9 kW

is used. The energy economy due to the use of FWD (EnEc1) can

be determined as the difference between the losses due to vessel

diameter in the absence of FWD and the sum of losses due to

vessel diameter in the presence of FWD and the power used to

obtain FWD.

The energy economy due to the use of mid-energy electron

beams and the use of FWD (EnEc2) also considers the reduction of

beam power losses (windows air) as compared to the situation

in which EBs of 0.7 MeV are used.

We should remember, however, that this application leads to

application of so called semi-wet process and the byproduct is in

the form of solution. The mist can be eliminated from the outlet

flue gases through condensation ESP application (Porowski et al.,

1995). To obtain solid state fertilizer (crystals) the water has to be

evaporated. This can be done in the humidification tower using

the heat of the inlet flue gases.

4. Conclusions

Electron beam accelerators most often applied for flue gas

treatment are those with medium electrons energy (o1 MeV) in

order to obtain low penetration depths ( 3 m). At this energy

level of electrons a significant level of electron beam power is lost

in the metallic foil windows and in the air gap between them. If

higher electron beam accelerators can be used (minimum

1.5 MeV), these losses would be significantly reduced. At this

level of energy, however, the penetration depth increases sig-

nificantly (approx. up to 7.5 m), which means that the treatment

of gases becomes due to the process vessel design difficulties.

However if FWD are added to the reaction mixture, the density of

this mixture increases largely, which determines the reduction ofthe penetration depth to reasonable values (23 m).

The overall efficiency of the process can be measured using the

energy efficiency (g pollutant/kWh of effectively used EB). The use

of this parameter allows us to compare the classical experiments

(in which only EB treatment was used) with the experiment in

which EB treatment in the presence of FWD was used at volu-

metric ratios liquid/gas between 0.0035 and 0.0096.

The presence of FWD determines the increase of the EB power

used, and the energy efficiency values obtained are higher than

the ones obtained in an industrial plant in which only EB

treatment is used.

When the power necessary to pump water in order to obtain

FWD is included in the total energy balance it can be noticed that

there is a limit value of the volumetric ratio liquid:gas (L). For a

higher amount of water it can be noticed that the energy needed

for obtaining FWD is higher than the economy of energy obtained

by using higher energy electrons. The optimal value of L is

function of the EB energy and of the maximum diameter of the

irradiation reactor.

The proposed solution requires some changes in the process

engineering since the mist has to be removed from the outlet

gases and then water evaporated to obtain solid product which is

fertilizer component.

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