Due to the different kiln body structure and thermal engineering process, intermittent kiln produces 5 times more flue gas than continuous kiln production. In general, the higher the gas temperature, the greater the proportion of heat loss. If the gas temperature is 1093 ℃, the heat loss reaches 55%; when the gas temperature is 1427 ℃, the heat loss reaches 70%. For the firing of refractory hot gas intermittent inverted kiln, according to the relevant experimental data show that: flue gas away from the kiln away from the heat about the furnace total heat expenditure of 35% to 40% in the absence of any heat recovery In the case of the measure, the heat balance calculation results, the thermal efficiency is only 10% ~ 15%. This is a big heat loss. Therefore, the use of flue gas heat is a very important energy recovery.
Set the heat exchanger in the flue is an important means of waste heat recovery. The hot air obtained after the heat exchange can be directly sent to the burner for combustion air, or the hot air can be diluted to the drying medium of the product embryo drying kiln or used to make the thermal efficiency of the kiln reach 30% or higher.
When the firing system uses a heat exchanger to preheat the air and use this hot air to make the combustion-supporting combustion air, the thermal efficiency of the kiln can be improved, the fuel consumption can be reduced, and the energy-saving effect can be achieved. And in the organization of high temperature combustion flame temperature can increase, increase heating efficiency, shorten the heating time (firing cycle). And because the hot air volume expansion, resulting in the burner orifice flow rate increases, accelerating the kiln gas circulation, contribute to the kiln temperature uniformity. The data show that: when the preheated air temperature reaches 220 ~ 250 ℃, can reduce fuel consumption by 6% to 8%. At the same time different combustion temperature, the impact on the flame temperature is very large. Even when the gas is not preheated, the combustion temperature of the gas increases significantly as the preheating temperature of the combustion air increases. This not only can solve the problem of low firing temperature, but also plays an important role in saving energy and reducing consumption.
In intermittent kiln production, because the fuel is changed with the heating stage, the amount of flue gas generated by the fuel also changes. In the event of a large fire, since the amount of fuel per unit time increases, the flue gas and temperature also inevitably increase. Preheat air combustion just to meet the requirements of combustion. Metal pipe heat exchangers are commonly used in production. Due to the limitations of high temperature oxidation and mechanical properties, the maximum service temperature is generally limited to below 500 ° C because of their low life (about 0.5 years). Metal pipe aluminum treatment, its service life is only about a year. The use of heat-resistant stainless steel or heat-resistant cast iron, the maximum temperature is generally limited to below 900 ℃. However, due to its high price, the use of units unbearable. 1. Because the fuel is the producer gas, the chimney bricks will not block. Life can be more than 10 years. Designed to ensure that the heat transfer efficiency, heat transfer area as large as possible (such as a group of 4 × 200m3 Square inverted hearth heat exchange area of ??about 230m2), although the volume is large, but the site conditions permit a one-time investment in the province, the flue System resistance is generally about 147 ~ 196Pa, chimney can be selected according to the height (usually about 50m).
The use of heat exchanger temperature is a very important factor in heat recovery. If the flue gas temperature is 1315 ℃, the use of thermal efficiency of 60% ceramic heat exchanger can save about 48% of fuel, if the use of thermal efficiency of 60% metal heat exchanger, you must first add cold air flue gas temperature dropped to 815 ℃ below, so that only 24% of fuel savings. Table 1 shows the effect of blending cold air on fuel economy.
In order to play the respective advantages of ceramic and metal heat exchangers, the two are used in tandem, known as a hybrid heat exchanger. First high-temperature flue gas into the ceramic heat exchanger, flue gas temperature dropped to below 815 ℃, and then into the metal heat exchanger. The flow of cold air is first into the metal heat exchanger, the heated air and then into the ceramic heat exchanger for further heating, the final preheated air temperature up to 1093 ℃.