NOx Reduction

General

Nitrogen oxides (NOx) emitted from burining fossils fuels(Coal, natural gas or oil) has been a main pollutant to contruibute to acid rain, urban smog, visibility impairment and global climate changes. The NOx reducing technology has been developed in Germany and Japan, Mid 1970`s. In recent years, many other countries have increased attention to NOx emission prevention. The technology called 'Selective Catalyst Reduction' or SCR is one of the most efficient way to remove NOx.

Soures

Mobil Soures (40%)

• Car, Truck, Air plane etc

Stationary Sources (60%)

• Fuel Combustion
• Power Plant
• Incinerator, etc.

Applications

• Gas turbines
• Nitric Acid Plants
• Waste Incineration
• Refinery Heater
• Ethylene Crackers etc.

Control of DeNOx

• SCR : At low operating temperature (200-450��, the reducing agent such as Ammonia(NH3) or Urea mix with NOx Gas and forms harmless nitrogen(N2) and water(H2O). During passing through catalyst layer
• SNCR : At high operating temperature (800-850��, the reducing agent such as Ammonia(NH3) or urea mixes with NOx Gas forms harmless nitrogen (N2) and water(H2O) without catalytic reaction. SNCR is more economical way to remove NOx in the range of 40~60 percent removal rate.The performance of SNCR can be reduced by operating in non complete mixing of NOx and NH3 or urea at improper temperature

Comparison SCR and SNCR

Operation Principal of SCR

Entering the NOx reductuin chamber the incoming air is mixed with required amount of Ammonia or Urea, homogeneously

As the incoming air flows pass through the catalyst layer, NOx react with Ammonia or Urea on the surface of the catalysts and form harmless Nitrogen(N2) and water(H2O)

4NO + 4NH3 + O2 → 4N2 + 6H2O

2NO2 + 4NH3 + O2 → 3N2 + 6H2O

Pre-heater is installed to heat the air steam up to optimum operating temperature (200~400��

To reduce the operating costs the abator unit has a recuperative heat exchanger bullt in, by which outgoing air is to heat the incoming air steam

Constituents and Feature of Catalyst

Consideration in theDesign SCR

• No influence on operation of the existing processes due to building SCR system
• Proper reaction temperature : 200~450��/li>
• Enough mixing reducing agent and NOx : Homeogeneously mixing
• Minimization of a pressure loss at catalyst layer
• Proper concentration of oxygen in the reaction chamber
• NH3 : ratio of NH3/ NOx increase till 1, and slow reaction after 1. Make ratio of NH3 and NOx should be 1. Excessive injections of NH3 cause the rate of NH3 slip
• Concentration of SO2 : The SOx material easily react with NH3 or one of other catalyst material and form anti-activated componets
• Dust
  • Low dust : No consider durability of catalyst against SO2
  • High dust : Required high durabiliable catalyst against SO2 and dust

Required Design Factor

• Gas volume
• Gas Composition
• Operating Temperature
• Maximum required level of NOx
• Rateof NH slip
• H2O Content

Advantage of the SCR System designed by TYMAGIC and LESNI A/S

Usage of catalyst, which has the most efficent performance, produced by BASF. Design capability of SCR required operating temperature and low Dust/High Dust etc. Design technology of the SCR package system containing heat exchanger and steam heater, etc. Ability of supplying the catalyst for Dioxin control. Experience in contruction of SCR system in power plant, Incineration plant, and chemical plant