Reduction of dust emission by Coromax micro-pulse power supplies at an oil shale fired power plant

doi:10.1016/j.elstat.2020.103447

Journal of Electrostatics

Volume 105, May 2020, 103447

https://doi.org/10.1016/j.elstat.2020.103447 Get rights and content

Highlights

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On an electrostatic precipitator, the existing switch-mode power supplies were replaced with micro-pulse power supplies.
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This resulted in halving the dust emission.
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This also resulted in almost halving the power consumption.

Abstract

Several classes of power supplies for ESP exist and the choice of the correct class is related to the resistivity of the dust to filter. The case of a power plant with high-resistivity dust emissions, for which the replacement of the existing power supplies with micro-pulse power supplies has succeeded in halving the dust emission level, is presented. The presentation is completed with data measured before and after the installation of the new power supplies and with a simplified analytical explanation supporting the results.

Introduction

This paper deals with the case of the oil-shale fired power plant, Balti Power Plant (hereinafter the Plant) near Narva in Estonia, owned by Eesti Energia.

Estonia massively uses oil shale, an organic-rich fine-grained sedimentary rock with a caloric heating value lower than hard coal and with higher ash content than lignite, for electricity production. The oil shale is burned in traditional boilers and the fumes are dedusted by electrostatic precipitators (ESPs) [1].

The three main typical voltage waveforms used in energization of ESPs are constant or almost constant voltage, voltage with grid-frequency ripple and voltage with microsecond-range pulses (Fig. 1).

These voltage waveforms need to be adapted to the resistivity of the dust to be filtered: typically, a constant or almost constant waveform is used for low-resistivity dust ( $ρ < 1 \cdot 10^{- 7} Ωm$ ), a grid-frequency ripple waveform is used for medium-resistivity dust ( $1 \cdot 10^{- 7} Ωm < ρ < 5 \cdot 10^{- 9} Ωm$ ) and a micro-pulse waveform is used for medium and high-resistivity dust ( $ρ > 5 \cdot 10^{- 9} Ωm$ ) [2,3].

Different classes of power supplies are used to create the required voltage waveforms as summarized in Table 1 [4].

Transformer/rectifier (T/R) sets, switch mode power supplies (SMPS)—often referred to as high-frequency power supplies—and voltage source converter (VSC)—often referred to as medium-frequency power supplies—can technically all provide the two waveforms adapted for low and medium resistivity.

Because of the large electrical time constant typical for an ESP—in the order of several milliseconds—, microsecond-range pulses can only be created by a special class of power supplies, here referred to as micro-pulse power supplies (MPPS). These are special power supplies, composed of two independent power supplies coupled by a resonant circuit [4,5].

In some cases of medium-high resistivity dust and under some limitations, it might still be possible to use single-phase T/R sets or SMPSs using the intermittent energization (IE) control technique [5].

At the Plant, substituting three SMPSs with three MPPSs succeeded in achieving the required low emission level, which otherwise could not be reached because of the high resistivity of the ashes.

In the Materials and Methods section, the description of the ESP in the Plant before and after the installation of the MPPSs is presented. It is completed by measurements of the original operation of the ESP. The section also includes the mathematical analysis used in the calculation of the power consumption and in the comparison of the ESP efficiency for the different classes of power supplies.

The Results section contains the measurements of voltage levels and power consumption obtained after the installation of the MPPSs, and the comparison with the original values. It also contains the measurements of dust emission levels and the comparison with the original values. The total mass efficiency of one section of the ESP for the different classes of power supplies for one specific case is also traced.

The Discussion and Conclusion sections follow, where the results are commented.

Section snippets

Materials and methods

This section is divided into four parts. The first part describes the setup of the plant and of the ESP under consideration, with its history. The second part is an analytical derivation of the equations linking ESP power and ESP mean voltage in the most generic case for SMPSs and MPPSs. The third part is an analytical derivation of the equations linking ESP filtration efficiency and ESP mean and peak voltages in the most generic case for SMPSs and MPPSs. The fourth part is an analytical

Results

This section is divided into two parts. The first part describes the operation of the ESP after the installation of the MPPSs. The second part presents the plots of the analytical functions of peak voltage and filtration efficiency versus mean voltage for a generic case, where the values of the constants introduced in the previous sections have been chosen to highlight the differences between the power supplies.

Operation of the ESP with MPPS — The operating electrical values for all the power

Discussions

The peak secondary voltage for the sections with MPPSs was much higher than the peak secondary voltage for the section with SMPS, and for the same sections before the installation of the MPPSs for the same operating conditions. The same peak secondary voltage on the first section, where the SMPS had not been changed, is an indicator of having compared the ESP under similar operating conditions.

In general, under the same operating conditions, and, therefore, under the same electrical conditions

Conclusion

This paper dealt with the case of an oil-shale fired power plant, for which changing the power supplies of an ESP from switch-mode power supplies (SMPSs) to micro-pulse power supplies (MPPSs) has halved the dust emission level. At the same time, this has also yielded a reduction in power consumption. The configuration of the ESP together with the operational data before and after the installation of the MPPSs has been presented. A simplified analytical explanation of why MPPSs have higher

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

Thanks are due to Jevgeni Ossovik and Jelena Derbneva of Eesti Energia AS for providing useful information and comments.

References (8)

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Geology and resources of some world oil-shale deposits: U.S
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(2006)
H.J. White
Industrial Electrostatic Precipitation
(1963)
V. Reyes et al.
Use of three-phase rectifiers in ESP's for low resistivity applications
N. Grass et al.
Application of Different Types of High-Voltage Supplies on Industrial Electrostatic Precipitators
(2004)

There are more references available in the full text version of this article.

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View full text

Reduction of dust emission by Coromax micro-pulse power supplies at an oil shale fired power plant

Highlights

Abstract

Introduction

Section snippets

Materials and methods

Results

Discussions

Conclusion

Declaration of competing interest

Acknowledgments

Geology and resources of some world oil-shale deposits: U.S

Geol. Surv. Sci. Invest. Rep.

Industrial Electrostatic Precipitation

Use of three-phase rectifiers in ESP's for low resistivity applications

Application of Different Types of High-Voltage Supplies on Industrial Electrostatic Precipitators