Experimental Study of Preheated Secondary Air on the Performance of an Updraft Coal Heating Stove

Although the Chinese government encourages using clean fuels for heating, many households in remote areas still rely on coal as their energy, especially in the Qinghai Tibet Plateau. An updraft coal heating stove was modified to preheat secondary air. The performance of the modified stove was studied compared with a baseline stove. The temperatures in the combustion chamber and near the chimney exit are measured, and the undiluted exhaust concentrations of CO, NO , and SO₂ are obtained. The results indicated that the temperatures and exhaust gas concentrations varied periodically with the coal addition. The oxygen concentration in the flue gas for the modified stove is higher than that for the baseline stove, and the O₂ concentration was decreased with the increase in fuel feed rate. The CO concentration peaked 5-15 min after fuel addition and descended quickly toward a baseline with the higher fuel feed rates. It remained almost unchanged at the beginning and then slightly increased when the combustion began to fade with a lower fuel feed rate for the modified stove. The NO emission for the modified stove is generally lower than that for the baseline stove. The NO formation during coal combustion mainly comes from prompt NO and fuel NO, while the SO₂ emission is mainly related to the sulfur element in the raw coal in the present work. The modified stove is effective in reducing NO and SO₂ emissions. However, the CO emission of the modified stove is higher than that of the baseline stove, especially at the end of the batch.