Hidekatsu Fujishima

Pilot-Scale

Pilot-scale simultaneous NO_x and SO_x removal from boiler emission was performed using an indirect-plasma and chemical hybrid process. The flue-gas flow rate was in the range of 450-1470 Nm³/h, the gas temperature was 280°C, the NO_x concentration was 30 ppm for city-gas firing, and both NO_x and SO_x concentrations were 70 and 35 ppm for heavy-oil firing, respectively. Radical injection by an indirect plasma was demonstrated to be extremely effective for NO oxidation, particularly when the flue-gas temperature is in the range of 300°C where NO_x is generated at this temperature. The produced NO₂ was further reduced to N₂ and nontoxic and water-soluble Na₂SO₄ by a Na₂SO₃ chemical scrubber. For the case of oil-firing boiler, SO₂ was simultaneously adsorbed by NaOH solution. The NO_x removal efficiency for gas firing exceeds 90%, but the NO_x removal efficiency for oil firing was in the range of 60% due to the lack of ozone concentration with the present pulse power supply. The removal efficiency of SO₂ was in the range of 85%-90%. The NO_x removal efficiency was evaluated by the ratio of the radical flow rate to the primary flue-gas flow rate, specific energy density, Na₂SO₃ concentration and chemical flow rate. Finally, the quality of disposed water was also investigated and proved to be disposable.

\hbox{NO}_{\rm x}

The three-dimensional flow interaction between the primary flow and the secondary flow (often called an electric wind or ionic wind) for tuft/point corona in the wire-duct type electrostatic precipitators (ESPs) has been investigated in the past. This study was further extended to incorporate the alternately oriented point corona on the wire-plate type electrodes, which are commonly used for the industrial ESPs. The secondary flow distribution without gas flow consists of a pair of long-elliptic and circulatory cells between spikes points along the wire. However, the flow rotation between spiked points is the same direction, which is opposite to that of the point corona electrode. The flow interaction is described using dimension-less number, N/sub EHD/, which is the ratio of the ionic wind velocity to the primary flow velocity. When the primary flow exists, a pair of long-elliptic spiral flows is formed in the direction of the gas flow between ground plates. When the relative distance between the spike point spacing and the wire-to-plate spacing (or the ratio of S/sub z//d) is greater than 0.17, the organized long-elliptic spiral flow is formed. When S/sub z//d is less than 0.1, the organized spiral flow is diminished, resulting in turbulence.

and

The process of removing NO_x from the flue gas emitted from a smoke-tube boiler was investigated using an ozonizer, which is used for carrying out the indirect oxidation of NO, and a Na₂SO₃ chemical scrubber. The flow rate of the flue gas was in the range of 410 - 1480 N·m³/h, its temperature was in the range of 185°C- 325°C, and the concentration of NO_x was approximately 40 ppm during the combustion of city gas. Operational and performance data were obtained from the experiments. The efficiency of the NO_x removal process was clearly dependent on the oxidation reduction potential (ORP), and it increased with a decrease in the ORP of the scrubbing solution. To effectively remove the requisite amount of NO_x, it is essential to maintain the ORP by controlling the injection rates of the Na₂SO₃ solution and maintaining an ORP of less than 0 mV and the rate of change in ORP to less than 0 mV/min. More than 4 kg/h of Na₂SO₃ must be added to the scrubber in order to sustain the aforementioned ORP condition of the scrubbing solution. The amount of NO_x emitted from the flue gas was maintained as less than 4 ppm at a flue gas flow rate of 410 N ·m³/ h during a 300-min continuous system operation by maintaining an ORP of -30 mV and a pH of more than 7.8 for the scrubbing solution.

\hbox{SO}_{\rm x}

NO_x removal from the flue gas of a smoke tube boiler using an ozonizer for NO oxidation and a Na₂SO₃ aqueous solution scrubber (diameter: 0.6 m; height: 3.7 m) was investigated. In this paper, in order to determine the correlation NO_x removal performance, the height of the packing material layer in the scrubber was varied from 2.1 to 0 m. The performance tests were carried out using both a compressed natural gas (CNG) and a heavy oil. The flue gas flow rates were in the range of 455-1440 Nm³/h under CNG firing and 675-1330 Nm³/h under heavy oil firing, and the boiler NO_x emission concentrations were approximately 40 and 100 ppm, respectively. A total packing height of 0.75 m resulted in NO_x removal efficiencies of 70% and 60% for CNG and heavy oil, respectively. Moreover, the Na₂SO₃ consumption rate at 0.75 m was 10%-20% less than that at 1.2 m, although the NO_x removal efficiency was nearly the same. The correlation between the NO_x removal performance and the gas retention time in the scrubber was obtained, providing the design information of the scrubber for industrial applications.

Removal From Boiler Emission Using Indirect-Plasma and Chemical Hybrid Process

The pilot-scale simultaneous NO/sub x/ and SO/sub x/ removal from boiler emission was performed using an indirect plasma and a chemical hybrid process. The flue gas flow rate was in the range of 450-1,470 Nm/sup 3//hr, the gas temperature of 280 /spl deg/C, and NO/sub x/ concentration of 30 ppm for city gas firing, and 70 ppm of NO/sub x/ and 35 ppm of SO/sub x/ for heavy oil firing, respectively. The radical injection by the indirect plasma was demonstrated to be extremely effective for NO oxidation especially when the flue gas temperature is in the range of 300 /spl deg/C where NO/sub x/ is generated at this temperature. The produced NO/sub 2/ was further reduced to N/sub 2/ and nontoxic and water soluble Na/sub 2/SO/sub 4/ by Na/sub 2/SO/sub 3/ chemical scrubber. For the case of oil firing boiler SO/sub 2/ was simultaneously adsorbed by NaOH solution. The NO/sub x/ removal efficiency for gas firing exceeds 90% but NO/sub x/ removal efficiency for oil firing was in the range of 60% due to the lack of ozone concentration with the present pulse power supply. The removal efficiency of SO/sub 2/ was in the range of 85-90% The NO/sub x/ removal efficiency was evaluated by the ratio of the radical flow rate by the indirect plasma to the primary flue gas flow rate, specific energy density, and Na/sub 2/SO/sub 3/ concentration and chemical flow rate. Finally, the quality of disposed water was investigated and proved to be disposable.

Numerical simulation of three-dimensional electrohydrodynamics of spiked-electrode electrostatic precipitators

ABSTRACT In this study, we propose a plasma-chemical hybrid NOx removal process using nonthermal plasma for the treatment of flue gases emitted from glass melting furnaces; the process is demonstrated through a laboratory-scale model experiment conducted using a semi-dry desulfurization apparatus. The performance of the system for simultaneous removal of SO2 and NOx is investigated. As a result, NO is effectively oxidized to NO2 by injecting ozone into the spray region and the removal efficiencies of 90% and 50% were obtained for NO and NOx, respectively. In addition, the SO2 removal efficiency of 84% was achieved.

Performance Characteristics of Pilot-Scale Indirect Plasma and Chemical System Used for the Removal of

A pilot-scale low-emission boiler system consisting of a bio-fuel boiler and plasma-chemical hybrid NOx removal system is investigated. This system can achieve carbon neutrality because the bio-fuel boiler uses waste vegetable oil as one of the fuels. The plasma-chemical hybrid NOx removal system has two processes: NO oxidation by ozone produced from plasma ozonizers and NO2 removal using a Na2SO3 chemical scrubber. Test demonstrations of the system are carried out for mixed oils (mixture of A-heavy oil and waste vegetable oil). Stable combustion is achieved for the mixed oil (20 – 50% waste vegetable oil). Properties of flue gas—e.g., O2, CO2 and NOx—when firing mixed oils are nearly the same as those when firing heavy oil for an average flue gas flow rate of 1000 Nm3/h. NOx concentrations at the boiler outlet are 90 – 95 ppm. Furthermore, during a 300-min continuous operation when firing 20% mixed oil, NOx removal efficiency of more than 90% (less than 10 ppm NOx emission) is confirmed. In addition, the CO2 reduction when heavy oil is replaced with waste vegetable oil is estimated. The system comparison is described between the plasma-chemical hybrid NOx removal and the conventional technology.

\hbox{NO}_{\rm x}

A pilot-scale low-emission boiler system consisting of a bio-fuel boiler and a plasma-chemical hybrid NO_x removal system is investigated. This system can achieve carbon neutrality because the bio-fuel boiler uses waste vegetable oil (WVO) as one of the fuels. The plasma-chemical hybrid NO_x removal system has two processes: NO oxidation by ozone produced from plasma ozonizers and NO₂ removal using a Na₂SO₃ chemical scrubber. Test demonstrations of the system were carried out for mixed oils (mixture of heavy oil and WVO). A stable combustion was achieved for the mixed oil (20%-50% WVO). The properties of flue gas-e.g., O₂, CO₂, and NO_x -when firing mixed oils were nearly the same as those when firing heavy oil for an average flue gas flow rate of 1000 Nm³/h. The NO_x concentrations at the boiler outlet were 90-95 ppm. Furthermore, during a 300-min continuous operation when firing 20% mixed oil, a NO_x removal efficiency of more than 90% was confirmed. This is equivalent to less than 10 ppm at the scrubber outlet when the flue gas flow rate was 870 Nm³/h. In addition, CO₂ reduction when heavy oil was replaced with WVO was estimated. The system comparison is described between the plasma-chemical hybrid NO_x removal and the conventional NO_x removal.

From Boiler Emission

NO x removal from a smoke tube boiler flue gas was investigated using a commercial ozonizer for indirect NO oxidation and a Na2SO3 chemical scrubber. The flue gas flow rate was in the range of 410 Nm3/h-1480 Nm3/h, the gas temperature of 185°C–325°C, and NO x concentration of around 40 ppm in city gas firing. Operational and performance data were obtained. The NO x removal efficiency was clearly dependent on the ORP and increased inversely as the oxidation reduction potential (ORP) in the liquid decreased. To keep the specified NO x removal performance, it is essential to maintain the ORP properly by controlling additional Na2SO3 and NaOH solution injection. NO x emission of less than 4 ppm was attained at 410 Nm3/h for a 300 minutes system continuous operation by maintaining ORP of-30 mV and pH of more than 7.8.

Improvement in

The number of small boilers using city natural gas, heavy oil (HO), and waste oils has been increasing annually in Japan, and more stringent regulations for nitrogen oxides (NOx) emission are being anticipated to reduce environmental NOx concentration. Taking this into consideration, it is envisioned that a suitable flue gas treatment system for small boilers will be required. The author proposed a plasma–chemical hybrid clean technology, consisting of an indirect nonthermal plasma process and a wet-chemical treatment. The tested flue tube boiler has an original rotary burner for gas and/or oil and is operated using city natural gas, biomass oil, or HO. The boiler has a steam generation rate of 2.5 ton/h, and for the clean technology, two sets of silent discharge-type plasma ozonizers are employed to generate ozone. Using the combination of ozone injection and chemical scrubber for flue gas, NOx can be effectively decomposed to nitrogen and oxygen, thus purifying the resulting effluent. The amount of nitrogen monoxide (NO) removed is almost the same as the amount of the corresponding ozone required to oxidize NO to nitrogen dioxide (NO2) (1:1 stoichiometric ratio). Previously reported experimental data are also discussed in the paper. A NOx removal efficiency of more than 85% was achieved over an operating time of 23 h using city natural gas as fuel. Based on the concept of carbon neutrality, ~80% carbon dioxide (CO2) reduction or fuel saving is also possible using waste vegetable oil (WVO)/HO mixed fuels. This low-emission boiler system can be used in industry.