RITE - OSAKA TAISHO LABORATORY in Hitachi Zosen Corporation

(1) Objectives

In selective catalytic reduction technology on Vanadium / Titania catalysts, the De-NOxsystem is usually operated in 300〜450℃ But in ordinary small-sized boilers, the De-NOx catalyst cannot be installed in this temperature range by the lack of space.

The object of this investigation is to complete Low-Temperature De-NOx System technology without any gas heating. This system will be adopted to the De-NOx of tale-end exhaust where gas temperature is about 150〜200℃

(2) Investigation and Developments

1)Improvement of Low-Temperature De-NOx activity

According to the reaction mechanism, it is considered, NO/NO2 ratio has an influence on De-NOx performance and when NO/NO2=1 in exhaust, the catalyst has the highest activity. But in actual exhaust, NOx is usually consisted of NO (over than 90%) and small NO2.

For getting high De-NOx performance, we have to oxidize NO to NO2 by injection of oxidizing agent, for example.

To improve the De-NOx activity in low temperature range, we made the investigation about oxidation technology of NO to NO2.

2)Study of SOx poisoning in Low-Temperature

In low temperature, it is said that the adsorption of SO3 and/or H2SO4 on the catalyst surface make hardly deterioration on De-NOx activity, even when very small amount of adsorption.

It is hard to prevent the SO3 adsorption in low temperature, so we have to re-generate the SOx-poisoned catalyst at suitable interval based on SO3 concentration.

We made the investigation about the simple re-generation method during the operation of De-NOx system without any catalyst exchanging.

3)Pilot-Scale test in actual exhaust

By pilot-scale test in actual exhaust gas, we made the whole evaluation about the Low-Temperature De-NOx technology.

(3)　Results

1)Improvement of Low-Temperature De-NOx activity

In case of below 200℃ we found the De-NOx activity is 3 times higher for NO/NO2=1 than for NO2 or NO only.

Many technologies of NO-oxidation are well known in many literatures, and we evaluated that the oxidation by plasma is better, and the oxidation by the UV(ultra violet)-luminous catalyst using plasma technologies is the best. Because it is said that NO is mainly oxidized by plasma and that the oxidation cost is not so high.

We measured that NO is oxidized by UV-luminous catalyst, but the amount of NO-oxidation by this UV-luminous catalyst is not so high as that by plasma only. This result is different from any literature data, so it is possible to be our mistake for our experimental method.

2)Study of SOx poisoning in Low-Temperature

We found that complete re-generation of SOx-poisoned catalyst is accomplished by heating with low concentration NH3 existence, and we proposed the simple re-generation system without stopping the De-NOx operation.(We will call this technology HGB(Hot Gas Blow) system.) And we found that the De-NOx efficiency will be kept more than 4 years by HGB technology even in the exhaust including SOx.

3)Pilot-Scale test about Low-Temperature De-NOx in actual exhaust gas

Location : Higashi-Osaka City incinerator No.4 factory

Capacity : gas flow rate=1000Nm3/h

( 1/100 for actual exhaust gas flowrate)

Reaction condition :

Reaction temperature = 170℃BR> NOx = 70〜100ppm(with fluctuation in all time)

SOx = 10〜40ppm(changing in all time)

H2O = about 25% and other component HCl, etc.

(1) Instead of NO oxidation, NO2 is injected from NO2-cylinder and NO/NO2 ratio is controlled. We found that the De-NOx activity for NO/NO2=1 is 3 times higher than for NO2 or NO only, and this result is almost agreed with labo-scale data.

(2) In this operation period, the De-NOx activity is kept almost constant as initial.

(3) We try to oxidize NO to NO2 by the catalyst (Pt/alumina and Mn/titania) and the plasma oxidation system, but by both method, we cannot make the situation NO/NO2=1. We think that NO oxidation may be prevented by something impure in actual exhaust gas and highly water ratio.

We are sure, if the NO oxidation system is completed, the whole Low-Temperature De-NOx Technology is basely finished. So we have some intention to make the co-investigation with some plasma equipment maker on NO oxidation in actual exhaust by plasma, and we will continue the pilot-scale test over next years.