【Weekly Topic】How should the cross-sectional area of the furnace chamber, its volume, and its height change? (2-12)

In my opinion, the cross-section and volume should be increased, as it is difficult to ignite and has a high calorific value; this is done to make it easier to ignite and to prevent the formation of deposits

Increase the cross-sectional area and volume, reduce the furnace height; due to its low flammability and high calorific value, strive to achieve spherical combustion, maintain the combustion temperature, and increase the length of the flue.

For a boiler with fixed parameters and capacity, the heat released by the fuel in the furnace per unit of time is constant. Therefore, when qv is large, the furnace volume becomes small ； If the size is small, the furnace volume is large. If qv is too high, the furnace volume becomes too small; as a result, the coal powder stays in the furnace for a short time, leading to incomplete combustion. Additionally, with a small area for the water-cooling walls, the furnace temperature rises excessively, which can easily cause slag formation. If qv is too low, the furnace volume becomes excessive, resulting in low furnace temperatures, which is unfavorable for combustion. It also increases the cost of the boiler as well as the amount of metal required. The empirical data are shown in Table 5-4. As can be seen from the table, the more flammable the coal, the larger the allowable value of qv. With the same furnace volume, the furnace can be designed to be long and narrow or short and stout. The excessively long furnace chamber results in good flame filling, but the burner area suffers from slag formation due to the lack of sufficient water-cooled walls to cool the flue gases. An excessively short and stubby furnace chamber results in low temperatures near the burner, which is unfavorable for ignition; moreover, the flame cannot fill the furnace chamber properly, the coal powder stays there for a short time, and heat losses due to incomplete combustion increase. The general shape of the furnace chamber is usually determined by both the heat intensity per unit cross-sectional area of the furnace chamber and the heat intensity per unit volume of the furnace chamber. The thermal intensity of the furnace cross-section refers to the heat released per unit time per unit area of the furnace cross-section. When qv remains constant, a higher value for qA results in a smaller cross-sectional area Al, making the furnace longer and narrower; whereas a lower value for qA leads to a larger cross-sectional area Al, resulting in a shorter and wider furnace. The empirical data are shown in Table 5-5. Once the heat intensity per unit area of the furnace cross-section is determined, the cross-sectional area of the furnace can be calculated using equation (5-3). By dividing this value by the volume of the furnace, the average height of the furnace can be obtained; however, the width and depth of the furnace still need to be determined. Given the actual conditions in our country, low-volatility coal tends to be burned using DC burners arranged at the four corners. Such furnaces require that the width of the furnace chamber be equal to its depth; in other words, the width-to-depth ratio should be 1, with a maximum value not exceeding 1.2. High-volatility coals tend to use swirl burners arranged at the front wall or at both the front and rear walls. If the swirl burner is arranged on the front wall, the furnace depth cannot be too small, to prevent the flame from reaching the back wall and causing slag formation.

Just about to reply when I saw that a few people above had already given the answer