Operation of four-tube electrostatic precipitator during pellet combustion in small-scale heat source under varying inlet air mass flow rate

This article experimentally evaluates how inlet air mass flow rate affects heat output, gaseous emissions, particulate matter (PM), and the collection efficiency of a four-tube electrostatic precipitator (ESP) installed downstream of an automatic pellet boiler. Measurements were conducted at five fan settings corresponding to inlet air mass flow rates of 89.18–143.64 kg·h⁻¹, with the ESP mode (ON/OFF). Increasing air mass flow caused a slight reduction in heat output (from 8.6 to 9.9 kW for ESP-OFF and 8.6–10.3 kW for ESP-ON) and a strong increase in CO at 10% O₂ (from 609 to 1512 mg·m⁻³ for ESP-OFF and 494–1670 mg·m⁻³ for ESP-ON), while NOₓ at 10% O₂ remained within a narrow range (128–146 mg·m⁻³ for ESP-OFF; 128–145 mg·m⁻³ for ESP-ON). The ESP mode (ON/OFF) had no measurable influence on heat output, CO, or NOₓ trends. During ESP-OFF mode, total PM showed a nonlinear dependence on air supply and reached a maximum at fan setting 4 (total PM concentration at 10% O₂ was 21.35–28.77 mg·m⁻³). During ESP-ON mode, total PM at 10% O₂ decreased to 2.34–4.85 mg·m⁻³, yielding overall collection efficiencies of 81.48–91.24%, with the maximum efficiency (91.24%) at 128.92 kg·h⁻¹ (fan setting 4). Quadratic regression captured strong dependencies of heat output on airflow (R² = 0.88–0.98), CO (R² ≈ 1), and NOₓ (R² = 0.93–0.99). The results demonstrate that the four-tube ESP provides high PM reduction (> 80%) under varying air-supply conditions without systematically altering heat output or gaseous emissions trends.