Hyoungsup Kim

Application of pulsed spark discharge for calcium carbonate precipitation in hard water.

The effect of underwater pulsed spark discharge on the precipitation of dissolved calcium ions was investigated in the present study. Water samples with different calcium hardness were prepared by continuous evaporation of tap water using a laboratory cooling tower. It was shown that the concentration of calcium ions dropped by 20-26% after 10-min plasma treatment, comparing with no drop for untreated cases. A laser particle counting method demonstrated that the total number of solid particles suspended in water increased by over 100% after the plasma treatment. The morphology and the crystal form of the particles were identified by both scanning electron microscopy and X-ray diffraction. Calcite with rhombohedron morphology was observed for plasma treated cases, comparing with the round structure observed for no-treatment cases. It was hypothesized that the main mechanisms for the plasma-assisted calcium carbonate precipitation might include electrolysis, local heating in the vicinity of plasma channel and a high electric field at the tip of plasma streamers, inducing structural changes in the electric double layer of hydrated ions.

Note: An underwater multi-channel plasma array for water sterilization

A simple yet effective method to generate multi-channel plasma array in water is presented in this paper. Thin circular metal disks sandwiched between dielectric layers were used, allowing the production of large-volume underwater plasma array with higher stability. The system can be further scaled up by stacking multiple metal disks, making it suitable for large-scale industrial water treatment. Generation of UV and reactive species was identified by optical emission spectroscopy. Sterilization experiments were performed. Results show that the device was effective in deactivating E. coli in water over a wide range of initial concentrations ranging from 10(4) to 10(8) CFU/ml.

Mineral Fouling Control by Underwater Plasma Discharge in a Heat Exchanger

The excessive mineral contents in water circulation systems could cause severe fouling in heat transfer equipment. The present study investigated the effect of underwater pulsed spark discharges on the mitigation of mineral fouling in a concentric counterflow heat exchanger. Artificial hard water with calcium carbonate hardness of 250 mg/L was used with velocity ranging from 0.1 m/s to 0.5 m/s and zero blowdown. Fouling resistances decreased by 50― 72% for the plasma treated cases compared with the values for no-treatment cases, indicating that the pulsed spark discharge could significantly mitigate the mineral fouling on the heat exchanger surface.

Pulsed Multichannel Discharge Array in Water With Stacked Circular Disk Electrodes

A simple yet effective system using stacked circular disk electrodes is developed to generate pulsed multichannel discharge array in water. Images of the pulsed multichannel discharge generated in water were obtained by applying pulsed high voltage over thin circular metal disks sandwiched between a pair of dielectric disks. By stacking multiple circular disks, the present discharge array system can produce large-volume plasma desired for the treatment of a large volume of water.

Stretched arc discharge in produced water

The objective of the present study was to investigate the feasibility of stretching an arc discharge in produced water to increase the volume of produced water treated by plasma. Produced water is the wastewater generated by hydraulic fracturing of shale during the production phase in shale-oil or shale-gas exploration. The electric conductivity of produced water is in the range of 50-200 mS/cm, which provides both a challenge and opportunity for the application of plasmas. Stretching of an arc discharge in produced water was accomplished using a ground electrode and two high-voltage electrodes: one positioned close to the ground electrode and the other positioned farther away from the ground. The benefit of stretching the arc is that the contact between the arc and water is significantly increased, resulting in more efficient plasma treatment in both performance and energy cost.

Nonchemical Methods to Control Scale and Deposit Formation

This chapter describes physical (nonchemical) water treatment (PWT) methods, which include permanent magnets, solenoid coils, radio frequency electric fields, high-voltage capacitance systems (i.e., electrostatic devices), and catalytic materials. The operating principle of the PWT is to produce colloidal particles of mineral ions in water, a process that is called bulk precipitation. In recirculating cooling water, the colloidal particles grow, resulting in particulate fouling (i.e., soft sludge coating) on a heat exchanger surface instead of precipitation fouling (i.e., hard deposit). Thus, if and when there is a sufficient shear force in a heat exchanger to remove the soft sludge coating, the PWT can keep the heat exchanger surface scale free.

Application of pulsed spark discharge for precipitation of calcium carbonate and prevention of mineral fouling in heat exchangers

One of the challenges in the production of electricity is the cooling water management because the calcium content in circulating cooling water continues to increase with time as pure water evaporates. Thus, the excessive mineral contents in water circulation systems could cause severe fouling in heat transfer equipment. To avoid the catastrophic failure in condensers, the cooling water is discharged after 3 cycles at a rate of 10 million gallons a day in a 1,000-MW thermoelectric power plant. The objective of the present study was to investigate the feasibility of using plasma discharge in water to precipitate excess calcium for the prevention of mineral fouling in condensers. The plasma discharge used in the present study utilized microsecond duration pulse spark discharge in water with a voltage up to 30,000 V and a typical peak-peak current of 100 A.

Application of Pulsed Spark Discharge for Mitigation of Mineral Fouling in a Heat Exchanger

One of the challenges in the production of electricity is the cooling water management because the calcium content in circulating cooling water continues to increase with time as pure water evaporates. Thus, the excessive mineral contents in water circulation systems could cause severe fouling in heat transfer equipment. To avoid the catastrophic failure in condensers, the cooling water is discharged after 3 cycles at a rate of 10 million gallons a day in a 1,000-MW thermoelectric power plant. The present study investigated the effect of pulsed spark discharges on the mitigation of mineral fouling in a concentric counterflow heat exchanger. Artificial hard water with calcium carbonate hardness ranging from 250 to 500 ppm was used with velocity varying over a range of 0.1–0.5 m/s and zero blowdown. Fouling resistances decreased by 50–88% for the plasma treated cases compared with the values for no-treatment cases. SEM photographs showed particle with larger sizes for the plasma treated cases comparing to smaller but more organized particles for the no-treatment cases. The different structures of particles were associated with pulsed spark discharge assisted precipitation of calcium carbonate in oversaturated hard water. X-ray diffraction data showed calcite crystal structures for all cases.Copyright