Hiroshi Murakami

Molar ratio and energy efficiency of DeNO/sub x/ using an intermittent DBD ammonia radical injection system

Ammonia radicals are produced by a dielectric barrier discharge (DBD) in a chamber, called radical injector, which is separate from the chamber that NO gas flows. The radicals are injected into the mixing zone in NO gas flow field to decompose NO gas. The power source for generating the DBD is a one cycle sinusoidal (OCS) waveform so as to easily control the electrical power consumed in the DBD plasma. The fundamental frequency of the OCS power source is 150 kHz. Based on the molar ratio of ammonia particles to NO particles in a unit time, NO removal characteristics were discussed. By increasing the DBD consumed energy, the molar ratio approaches 1 showing the stoichiometric DeNO/sub x/ by NH/sub 2/ radicals. A high energy efficiency is found by reducing the consumed energy in the radical injector, where the molar ratio is higher than 1. In this case, the excess ammonia gas without converting into ammonia radicals in the radical injector is directly injected into the reaction zone, and contributes to decompose the NO gas. Oxygen gases with a concentration from 5% to 15% included in the NO gas significantly contribute to decompose NO gases, which brings a decomposition of NO with a low molar ratio.

Efficient Denox using an Intermittent DBD with One Cycle Sinusoidal Power Source

Summary form only given. Nitric oxide (NOx) gases are emitted from sources such as thermoelectric power plants and diesel automobiles. It is important to reduce them to preserve air environment. There are needs for the removal of NO gases, where a high efficient and maintenance-free NO/NOx removal system is demanded. The efficient NOx removal (DeNOx) system is expected to use plasma reactors, because plasma species have a high average energy enough to easily decompose NO/NOx species. We have already developed a radical injection system using an intermittent dielectric barrier discharge (DBD) produced by a power source with a one-cycle sinusoidal output. Ammonia radicals are produced in a separate plasma chamber from the reaction zone for DeNOx. An energy efficiency of 250 g/kWh was obtained. The system developed in this paper is based on the previously developed one. However, the different point is that NO is directly decomposed in the DBD plasma. By this, the system can be compact. This paper concerns a direct decomposition of NO gas, which flows through an intermittent DBD plasma generated by the same power source as the radical injection system. An energy efficiency of 100 g/kWh is attained, where the duty cycle of the power output is optimized. The power source with an intermittent output voltage is advantageous to easily control the consumed power. A parametric survey for the optimization of DeNOx is carried out for DeNOx. Several parameters are varied: applied voltage and its duty cycle, gas temperature, gas flow rate, NO concentration, concentrations of additive gases as ammonia, argon, and methane. In the case of direct decomposition of NO gas, oxygen contained in the NO/N2 gas flow significantly influences the DeNOx characteristics. In the previously-developed radical injection method, oxygen does not significantly influence the DeNOx characteristics, because oxygen is not activated. In the direct DeNOx system, in which oxygen-contained NO gas flows through the DBD plasma, oxygen is activated. The byproduct of DeNOx is mainly NO2. NO2 is hardly produced in the absence of oxygen, where NO may be decomposed to be N2 and O2. The excess of oxygen contained in the NO gas flow field contributes to prepare NO2 from N2 and O2. NO2 formation from N2 and O2 is confirmed by decomposition test of a simulated air (N2/O2 = 80/20%). By optimizing the parameters for DeNOx, energy efficiencies of 100 g/KWh and 50 g/kWh are obtained in the absence and in the presence of oxygen, respectively.

Paprametric survey on no removal in an intermittent di-electric barrier discharge by one-cycle sinusoidal power source

NO gas is directly decomposed using an intermittent dielectric barrier discharge (DBD). The power source for generating the DBD is a one-cycle sinusoidal (OCS) output so as to easily control the electrical power consumed in the DBD plasma. The fundamental frequency of the OCS power source is 150 kHz. As a parametric survey for finding an efficient NO removal, the influencing factors behaves as follows: Applied voltage: high but low is desirable, Gas temperature: high, Gas flow rate: low, Repetition rate: low, NO concentration: high, Additive gas: argon diluted ammonia with a high concentration, Consumed energy: high but low is desirable, Oxygen: none. Pursuing the optimization for the NO decomposition, the energy efficiency of over 80 g/kWh is obtained in the absence of oxygen contained in NO/N 2 gas.

Parametric Survey for Efficient DeNOx by Direct Decomposition of NO Using an Intermittent DBD Generated by a One-Cycle Sinusoidal Power Source

Abstract NO gas is directly decomposed using an intermittent DBD plasma generated by a one cycle sinusoidal power source. Previously, we have developed an ammonia radical injection system, where ammonia radicals were produced by a dielectric barrier discharge (DBD) in a chamber, called a radical injector, which is separate from the chamber in which NO gas flows. The radicals are injected into the mixing zone in the NO gas flow field to decompose NO gas. The power source for generating the DBD is a one-cycle sinusoidal (OCS) waveform so as to easily control the electrical power consumed in the DBD plasma. The fundamental frequency of the OCS power source is 150 kHz. In this paper, we used the same power source, but NO was decomposed directly by the plasma; that is, NO gas is in the DBD plasma. NO gas was varied from room temperature to approximately 400 C, where the effect of DeNOx characteristics were discussed. By optimizing parameters for DeNOx, an energy efficiency of 100 g/kWh was obtained.

Voltage and temperature effects of denox in dbd plasma generated by an intermittent power source

Summary form only given. We have developed a direct NO decomposition system using an intermittent power source, where NO is decomposed in a DBD plasma generated by an intermittent sinusoidal power source. The effects of applied voltage to generate a DBD plasma and gas temperature to the DeNOx rate are mainly investigated. This research is based on the ammonia radical injection DeNOx method using a same intermittent pulse power source. The consumed energy shows a linear increase with the applied voltage under the experimental conditions. The DeNOx starts near at an applied voltage of 18 kV for NO/N2 mixed gas, while the DeNOx initiates at 10-14 kV, when argon or argon diluted ammonia gases are added to NO/N2 gas flow field. Thus, the additive gas lowered the DeNOx initiation voltage. This means that NO is decomposed more efficiently by mixing these gases to the NO/N 2 gas. Furthermore, ammonia containing gas is more effective for DeNOx rate than argon gas. The gas temperature significantly influences the DeNOx rate, i.e., at an elevated temperature at 300 C, DeNOx is seen at lower applied voltage even for NO/N2 gas without the additive gas. The plasma reactor consists of a pair of coaxial electrodes with an outer diameter of 64 mm and a gap length of 1.5 mm. Both electrodes are covered with cylindrical quartz tubes. The effective plasma length is 350 mm. The system is in an electric furnace to elevate the gas temperature. The NO concentration is 1000 ppm with a flow rate of 1 L/min. The gas temperate is increased from room temperature to 300 C, and the voltage is increased up to 30 kVp-p