Electron Beam Dry Scrubbing Process Research Articles

Experimental evidence of nitrous acid formation in the electron beam treatment of flue gas

In the Electron Beam Dry Scrubbing (EBDS) process, flue gas from fossil fuel burning power plants is irradiated with accelerated (300–800 keV) electrons. Thereby, nitrogen oxide (NO x ) and sulfur dioxide (SO 2) traces are transformed into nitric and sulfuric acids, respectively, which are converted into particulate ammonium nitrate and sulfate upon the addition of ammonia. The powdery can be filtered from the main gas stream and can be sold as agricultural fertilizer. A lot of experimental investigations have been performed on the EBDS process and computer models have been developed to interpret the experimental results and to predict economic improvements. According to the model calculations, substantial amounts of intermediate nitrous acid (HNO 2) are formed in the electron beam treatment of flue gas. However, no corresponding experimental information is available so far. Therefore, we have undertaken the first experimental investigation about the formation of nitrous acid in an irradiated mixture of NO in synthetic air. Under these conditions, aerosol formation is avoided. UV spectra of the irradiated gas were recorded in the wavelength range λ = 345–375 nm. Both NO 2 and HNO 2 have characteristic absorption bands in this wavelength range. Calibration spectra of NO 2 were subtracted from the sample spectra. The remaining absorption bands can clearly be assigned to nitrous acid. The concentration of nitrous acid was determined by differential optical absorption. It was found lower than the model prediction. The importance of nitrous acid formation in the EBDS process needs to be clarified.

The influence of SO 2 and NH 3 concentrations on the aerosol formation in the electron beam dry scrubbing process

The electron beam dry scrubbing process simultaneously removes SO 2 and NO x from exhaust gases. In the presence of ammonia, ammonium sulfate and ammonium nitrate aerosols are formed. The removal yields and the aerosol composition have been characterized as a function of the SO 2, NO x and NH 3 concentrations. The data show that at higher SO 2 and NH 3 concentrations the nitrate and ammonium concentrations in the aerosol become saturated, despite increasing NO x removal yields. This indicates that reduction mechanisms forming N 2 and N 2O from NO x become important at high ammonia stoichiometries.

Removal of the aerosol formed in the electron beam dry scrubbing process by bag filters

Removal of the aerosol formed in the electron beam dry scrubbing process by bag filters

Dynamics of particulate formation in the electron beam dry scrubbing process

By electron beam treatment of waste gas, SO 2 and NO x are oxidized to nitric and sulfuric acid. Upon addition of ammonia, particulates are formed which can be filtered in dry state. Experimentally, the aerosol mass growth has been found to depend both on irradiation dose and on operating conditions. Model calculations have been performed to investigate the dose and relative humidity effects on particulate mass formation and aerosol size.

Aerosol formation in the electron beam dry scrubbing process (ES-Verfahren)

The aerosol formation in the electron beam dry scrubbing process depends mainly on the parameters dose, relative flue gas humidity and ammonia concentration. For the sulphate formation two pathways have been identified: One pathway is the radiation induced homogeneous SO 2-oxidation, yielding sulphuric acid. The second pathway is probably a heterogeneous sulphate formation mechanism in aerosol droplets. The efficiency of this mechanism depends on relative humidity, ammonia concentration and dose. Nitrate and ammonium concentrations in the aerosol depend also on dose and relative humidity. At higher ammonia-stoichiometry a saturation of the nitrate and ammonium concentrations indicates that reduction of NO x becomes important.

Progress in the electron beam treatment of stack gases

The Electron Beam Dry Scrubbing Process removes simultaneously SO 2 and NO x from exhaust gases forming solid Ammoniumsulfate and -nitrate in the presence of NH 3 which can be sold as fertilizer. Basic research on this process started 1970 at the Japan Atomic Energy Research Institute and at Tokyo University while the technical development was followed up by EBARA Corporation. A first pilot plant was built and operated in 1977. A second phase of intense development on the process started in 1983 in the USA and the Federal Republic of Germany. Initiated by legislative efforts in West Germany to reduce SO 2 and NO x emissions, the development of a low cost, flexible and simultaneous scrubbing process was promoted. Two technical scale Electron Beam research facilities and two pilot plants are in operation since 1984 resp. 1985 in Karlsruhe, Germany, and Indianapolis, USA. From these plants operating with flue gas from crude oil, gas and coal fired boilers numerous data are available. Extensive parameter measurements enable to identify the conditions where the process has high efficiencies.

The influence of SO 2 and NH 3 concentrations on the aerosol formation in the electron beam dry scrubbing process

Das Elektronenstrahlverfahren (ESV) ermöglicht die simultane Abscheidung von SO 2 und NO x aus Rauchgasen. Durch Bestrahlung mit schnellen Elektronen werden SO 2 und NO x bei Injektion von Ammoniak in Ammoniumsalz-Aerosole umgesetzt. Die Abscheidegrade für NO x und SO 2 und die chemische Zusammensetzung des Produktaerosols wurden in Abhängigkeit von der Rauchgaszusammensetzung (SO 2 und NO x Konzentrationen) und der Ammoniakstöchiometrie untersucht. Der Sulfar- und der Ammoniumgehalt des Aerosols nehmen erwartungsgemäß bei steigender SO 2-Konzentration zu. Dagegen ist der Nitratgehalt im Produktaerosol nahezu unabhängig von der SO 2-Konzentration. Mit steigender Ammoniakstöchiometrie nehmen die SO 2- und NO x-Abscheidegrade sowie die Sulfat- und Ammoniumkonzentrationen im Aerosol zu. Der Zusammenhang zwischen der Abscheideeffizienz des Verfahrens und Aerosolbildung wird diskutiert.

Physical and chemical properties of the aerosol produced by the electron beam dry scrubbing of flue gas (ES-Verfahren)

The ‘ES-Verfahren’ is an electron beam dry scrubbing process by which NO x and SO x is removed simultaneously from exhaust gases in the presence of NH 3. With respect to the industrial application of this process, particle formation and the physical and chemical properties of the product aerosol have been investigated under well-defined conditions in the pilot plant AGATE operating at the crude-oil-fired power plant of KfK. The chemical composition and size distribution of the product aerosol depends on a variety of process parameters such as composition of the exhaust gas, residence time in the system and applied radiation dose. The mass concentration of the reaction product aerosol was found to be 500–2500 mg m −3, depending on the operating conditions of the plant. Characteristic for the product particles are mass median diameters of 0.5–7.5 μm. The experimental results are in agreement with the assumption that acid droplets formed by condensation are subsequently neutralized by NH 3.