A microwave plasma potential in producer gas cleaning — preliminary results with a gas derived from a sewage sludge

The paper presents an attempt to evaluate the impact of coal and coal mine methane cocombustion on the physics of the heat exchange in an 140 t/h pulverized-coal boiler through an analysis of 21 combinations of the boiler operating parameters – three different boiler loads (50, 75, and 100%) and seven values of the fired gas thermal contribution (0–60%). The obtained results are the temperature distribution of flue gas and steam in the boiler characteristic points, the heat transfer coefficient values for the boiler individual elements expressing the nature of changes in the heat transfer and the change in the boiler efficiency depending on how much gas is actually fired. An increase in the amount of co-fired gas involves a temperature increase along the flue gas path. This is the effect of the reduction in the amount of heat collected by the evaporator in the furnace. For these reason, the flue gas temperature at the furnace outlet rises by 9 K on average per a 0.1 increment in the fired gas thermal contribution. The temperature rise improves the heat transfer in the boiler heat exchangers – for the first- and the secondstage superheater the improvement totals 2.8% at a 10 pp. increase in the fired gas thermal contribution. However, the rise in the flue gas temperature at the boiler outlet involves a drop in the boiler efficiency (by 0.13 pp. for a rise in the fired gas thermal contribution by 0.1).