Industrial experiments on desulfurization of flue gases by pulsed corona induced plasma chemical process

Journal of Electrostatics 57 (2003) 233–241

Industrial experiments on desulfurization of fluegases by pulsed corona induced plasma chemical

process$

Yan Wu*, Jie Li, Ninghui Wang, Guofeng Li

Institute of Electrostatics and Special Power, Dalian University of Technology, Dalian 116024, China

Received 12 December 2001; received in revised form 17 July 2002; accepted 26 August 2002

Abstract

Based on the large amount of data obtained in the laboratory, desulfurization studies of the

flue gases on industrial experiment scale by Pulsed corona induced Plasma Chemical Process

(PPCP) were accomplished. The flow rates of flue gases were 3000 and 12,000–20,000Nm3/h.

For a 1000–2000 ppm concentration of SO2, the removal rate of SO2 can be more than 80%

with the flue gas temperature 70–801C, water volume ratio 10%, resident time 5–8 s and energy

consumption 3–4Wh/Nm3.

r 2002 Elsevier Science B.V. All rights reserved.

Keywords: Pulsed corona discharge; Desulfurization of flue gas; Industrial experiment; Plasma chemical

process; Flue gas

1. Introduction

Desulfurization of flue gas is one of the main methods to control SO2 emission andacid rain. In the late 1980s, Masuda put forward a new method, PPCP, for SO2

removal in flue gas [1]. The method was proved to be competitive and promising bymany research works. It can be classified as a dry method for desulfurization and hasmany merits, such as removing SO2 and NOx simultaneously, and its byproducts can

$Original version presented at ICAES’2001, Fourth International Conference on Applied Electro-

statics, 8–12 October 2001, Dalian, China.

*Corresponding author.

E-mail address: [email protected] (Y. Wu).

0304-3886/03/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved.

PII: S 0 3 0 4 - 3 8 8 6 ( 0 2 ) 0 0 1 6 3 - 8

be used as fertilizer, etc. Furthermore, the initial investment and running cost arecomparatively low. Thus, many studies were carried out by researchers in manycountries, and good results were achieved, which promoted the desulfation techniqueby PPCP to the industrial scale experiment. Dinelli’s studies on industrial experimentscale show that, for a 100–1000Nm3/h flue gas, desulfation rate can be 80% and thedenitration rate can be 50–60% when the initial concentration of SO2 and NOx are530 and 400 ppm, respectively, and the energy consumption was 12–15Wh/Nm3 [2].In Mok’s research, the flow rate of the flue gas was 5000Nm3/h and the initialconcentration of SO2 and NOx was 350 and 400 ppm, when the energy consumptionwas 4Wh/Nm3 and the removal rate of SO2 was 90% [3]. In addition, Canada, SouthKorea and Russia are still studying this process on a wide scale and for a higher flowrate [4]. Chang got good results in their experiments of desulfation and denitration inthe way of corona radicals shower of the NH3 [5].

Under the support of Chinese Natural Science Foundation and Ministry ofScience and Technology, many researches had been carried out on the technology ofdesulfurization in flue gas with pulsed corona discharge in both fundamental andapplied field at the Institute of Electrostatics and Specific Power, China. Industrialexperiments of 1000–3000Nm3/h and 12,000–20,000Nm3/h flow rate were accom-plished and many satisfactory experimental results were obtained. The paper willintroduce the research results of two industrial experiments.

2. Basic principle

Active particles, ion, radical, etc. can be produced by pulsed corona discharge inatmospheric air. For example,

N2;O2;H2O; þ e�-OH;O;HO2;H2O2; etc:

These active particles can react with SO2 and NOx molecules. The possiblechemical equations are as follows:

NOþO-NO2

NOþO3-NO2þO2

NOþHO2-NO2þOH

NO2þOHþM-HNO3þM

SO2þO-SO3

SO2þOH-HSO3

HSO3þO2-SO3þHO2

SO2þHO2-SO3þOH

SO3þH2O-H2SO4:

Y. Wu et al. / Journal of Electrostatics 57 (2003) 233–241234

With NH3 existence, the chemical equations are

HNO3þNH3-NH4NO3

2NH3þSO2þH2O-ðNH4Þ2SO3

2NH3þSO3þH2O-ðNH4Þ2SO4

ðNH4Þ2SO3þO-ðNH4Þ2SO4:

3. The achieved results in laboratory

Many results, which are important to industrial experiment for SO2 removal, havebeen obtained in laboratory. The followings are the main results:

(1) Positive pulsed voltage is beneficial to SO2 removal [6].(2) The pulsed width should be in the order of nanosecond, the rise time of high

voltage pulse should be very short, and it is beneficial for the SO2 removal to usedirect current bias voltage at a certain extent [6].

(3) The temperature of flue gas should be in the range of 60–801C [7].(4) The resident time of flue gas in reactor should be about 10 s [8].(5) The relative humidity of the flue gas should be increased in a certain range [9].(6) The injected vapor that had been activated by corona discharge can increase the

SO2 removal rate [10].

4. The 1000–3000Nm3/h industrial experiments

4.1. Experimental apparatus

4.1.1. Pulsed corona discharge reactor for SO2 removal

The wire–plate electrode structure was used in the reactor. Taking account of peakvoltage of power supply and high voltage insulation, the reactor was designed tohave 5 channels. Each channel was 200mm in width. The 4� 4mm star shape wireswere used as discharge electrodes. By regulating the flue gas flow rate, the residenttime of flue gas in reactor can be regulated in the range of 5–10 s.

4.1.2. High voltage pulse power supply

Fig. 1 is the principal diagram of pulse power supply for experiment. The HVpulse power supply is 15 kW. It can continuously output pulses with peak voltage of120 kV, risetime less than 100 ns and pulse width 300–500 ns. The pulse repetitionrate is 50–200 pps. The direct current bias voltage is in the range of 10–20 kV. Bothpulse voltage and current waveforms are shown in Fig. 2.

4.1.3. Others

The system for SO2 removal in flue gas mainly includes precipitation part, cooling part,adding NH3 part and byproduct collecting part. Fig. 3 is the flowchart of the system.

Y. Wu et al. / Journal of Electrostatics 57 (2003) 233–241 235

Fig. 1. Circuit diagram.

t/500ns/div

V/2

0kv/

div

I/20

0A/d

iv

1

20 0

1 voltage 2 current

Fig. 2. Typical waveforms of voltage and current.

Boiler Precipitator Reactor

NH3 , water vapor

ESP

Pulse power supply

Chimney

Fig. 3. Flowchart of the system for SO2 removal with PPCP.


4.2. Main results

The industrial experiment for SO2 removal of flue gas was carried out utilizing the1000–3000Nm3/h flue gas processing system. The flue gas (O2, 8%; CO2, 12%; SO2,1000–2000 ppm and water volume ratio 10%) came from coal burning boiler. Themain experimental results were as follows:

(1) There is an appropriate distance between wire and wire, which has great effecton energy injection, energy efficiency, plasma distribution and finally the SO2

removal rate. Fig. 4 shows the distribution of the pulsed streamers for a differentwire distance. It can be obviously seen in the photos that the streamer areaincreased and the distribution of the streamer is much more uniform for a smallwire distance. In addition, experimental results show that as energy injected intothe reactor increased, the removal rate of SO2 improved.

(2) The power supply must match the reactor. If power and reactor do not match,pulse voltage waveform will be distorted and the energy efficiency will bedecreased. Furthermore, spark discharge occurs frequently and the reactor willnot work properly.

(3) The risetime of pulse voltage should be short as much as possible and not lessthan 1 kV/ns. With the same injection energy, decrease of pulsed width andincrease of pulse repetition rate are beneficial to the removal of SO2.

(4) The increase of H2O volume ratio in flue gas is beneficial to SO2 removal. Thus,it is necessary to inject certain amount of vapor into flue gas. This will increasethe SO2 removal rate. The SO2 removal rate will be increased 10% if the vaporwas processed by corona discharge before was injected into the reactor. Fig. 5shows the SO2 removal rate with the water vapor added.

(5) The relation between the resident time of flue gas in reactor and the SO2 rate isshown in Fig. 6. The resident time of flue gas in reactor has great effect on SO2

removal rate and the investment of equipment. By taking account of these twoaspects, the optimized resident time is 5–6 s.

(6) The result of 1000–3000Nm3/h PPCP flue gas desulfurization experiment is thatthe removal rate of SO2 is 80–85% when the initial concentration of SO2 is1000–2000 ppm, the temperature of flue gas of 65–751C, the water volume ratio10%, the stoichiometric ratio of SO2 to NH3 1:1, the resident time of flue gas inreactor 5–6 s and the injection energy 2.5–3.5Wh/Nm3.

Fig. 4. Streamers distributing of pulse discharge: (a) Distance among wires and wires 5 cm, (b) Distance

among wires and wires 10 cm.


5. Desulfurization experiments of 12,000–20,000Nm3/h flue gas

Based on the satisfactory results of above experiments, the desulfurizationexperiments of 12,000–20,000Nm3/h flue gas PPCP were carried out in order toperform larger-scale industrial experiments. The aims are to find and solve theproblems in the enlarged experiments and to accelerate the progress of industrialapplications for flue gas desulfurization by the method of PPCP.

5.1. Experimental system

Experimental system includes cooling tower, NH3 injecting system, installing thedischarge activation equipment of vapor, reactor, HV pulsed power supply,byproducts collection installation as well as control and measurement system.Fig. 7 is the flowchart of the experimental system.

60

65

70

75

80

85

90

95

4 6 8 105 7 9

H2O/%

η/%

without activity

with activity

Fig. 5. Relationship between water content and efficiency of DeSO2.

50

60

70

80

90

3 7 115 9

t/s

DeS

O2

η/(%

)

Fig. 6. Relationship between resident time and efficiency of DeSO2.


Vapor activation part and reactor were designed as one bulk. The wire–platereactor was designed with two electrical field sections. Each section used one pulsedpower supply. The electrostatic collector was used to collect the byproduct. The steelbrush used to clean the ash was designed to clean away the collected byproducteasily.

Pulsed power supply used switch type of magnet compression. Its principle isshown in Fig. 8. Output power of power supply is 50 kW. Risetime is less than100 ns. Frequency can be regulated in the range of 50–500 pps. Pulse width is in therange of 300–500 ns. Direct current bias voltage is 15 kV.

5.2. Experimental results

One part of the flue gas of a 3000 kW coal fired power plant was used as thetreated gas.

The main composition of the flue gas is: 10–12% CO2, 1000–2000 ppm SO2,200–800 ppm NO and the dust concentration of 300 g/m3. Through the 12,000–20,000Nm3/h experiment of the desulfation the results are as follows: under the

SO2

NO

Cooling Tower

Reactor ESP

Pulsepower

NH3 Adding

Measuring Controlling

Flue Gas

Chimney

Fig. 7. Flowchart of experimental system.

Fig. 8. Schematic of pulsed HV power supply with magnetic compression switch.


condition of initial concentration of SO2 of 1500–2000 ppm, flue gas temperature of70–751C, water volume ratio of 10%, the resident time of 6–8 s, the stoichiometricratio of SO2 to NH3 of 1:0.9–1:1, pulse power of 3–4Wh/Nm3, the removal rateof SO2 more than 80% and collection rate of byproduct ammonia sulfate morethan 99%.

The concentration of NOx and NH3 in the effluent were tested in the experiment.Under the above-mentioned conditions, the NOx removal rate can be at least 50%and the concentration of the NH3 in the treated gas is less than 50 ppm.

6. Conclusions

Industrial experiments of 1000–3000 and 12,000–20,000Nm3/h flue gas flow PPCPdesulfurization were carried out and satisfactory results were obtained. The valuabledata were put forward for continuation of research and industrial application. Theinvestment of PPCP flue gas desulfurization apparatus is approximate to the 10% ofthe investment of power plant. The running cost is about $60 for the removal of oneton of SO2. Therefore, the desulfurization technology of PPCP has a greatcompetitive power in the market.

The larger-scale experiments should be carried out for flue gas desulfurizationtechnology of PPCP in order to reach the industrialization application stage as soonas possible. Furthermore, the following two questions should be solved as much aspossible:

(1) The research and development of HV pulse power supply that can be used inindustrial application.

(2) The optimization of pulsed corona induced plasma characteristics and theoptimal design of PPCP reactor. The two aspects mentioned above concernedwith the increase of efficiency of desulfurization and energy utilization rate.

References

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Documents

Industrial experiments on desulfurization of flue gases by pulsed corona induced plasma chemical process