Design of an electrostatic precipitator for a novel bituminous coal-fired circulating fluidised bed combustion power plant in Namibia

Abstract

Coal-fired power plants utilising fluidised bed technologies emit copious amounts of fly-ash, which is harmful to people owing to its particulate nature. A planned 300 MW power plant will have an electrostatic precipitator (ESP) for fly-ash emissions control, in line with power generation industry best practices. This ESP should meet a fly-ash emission limit value ≤ 50 mg/Nm³. This paper details the design process and resultant technical specifications of a cold-side, single-stage, and plate-wire dry ESP designed for the power plant. The ESP will consist of twin-chambers with quadruple-fields (2 4 315 m³) and octonary bus-sections independently energised by individual high-frequency three-phase switched integrated rectifiers (70 kV, 800 mA) to maximise ionisation. Dynamically balanced, single-impact, tumbling hammer rappers (857.5 rpm) will dislodge fly-ash from the collector plates into mass-flow wedge-shaped hoppers. A specific collection area (≥ 56.9 m²/m³/s) and an ESP index (≥ 709.2 (kV/cm)²m²/m³/s) should guarantee a collection efficiency (  ≥ 99.5 %) and the specified emission limit value at 100 % boiler capacity and normal operating conditions (gas velocity ≤ 2.4 m/s; gas temperature ≤ 137 ℃; fly-ash loading ≤ 10 000 kg/Nm³; resistivity ≤ 10¹⁰ Ω‧cm). The design was successfully verified in principle using the validation square method, in conjunction with the leading comparable historical case studies approach. It is recommended to simulate ESP designs using suitable programs like Comsol Multiphysics and construct a pilot plant before attempting scaled-up construction and commissioning.

Highlights          

• A cold-side, single-stage plate-wire dry ESP system designed.
• Theoretical collection efficiency in excess of 99.5%.
• High-frequency, three-phase switched integrated rectifiers to be used for ionisation.