Energy saving measures of gas industrial furnace

In 2010, at the first China International Gas Energy Summit and the International Forum on the bio natural gas industry, relevant experts and scholars expressed that "China will enter the era of gas energy". As an important part of clean energy, "gas energy tourism" will gradually become the mainstream of energy consumption in the 21st century. Especially in China, where the economy is developing at a high speed, the proportion of primary energy consumption is seriously out of balance, the high dependence on oil import and the high carbon emission have become a huge shackle hindering the continuous high-speed development of China's economy. Therefore, the development of "gas energy" is accelerating from all over the country. Among them, gas industrial furnace refers to the heating furnace and heat treatment furnace using gas fuel. Because the combustion characteristics of gas fuel are different from that of solid fuel or liquid fuel, the energy-saving measures of gas industrial furnace are not exactly the same as those of solid fuel and liquid fuel.

In the industrial furnace, the heat of the object is obtained by conduction, convection and radiation heat transfer. 

However, for the gas industrial furnace, 60% - 70% of the total heat obtained by the object is from the radiation heat transfer of the furnace lining, not the radiation of the flame. It can be seen that the radiation emission performance of the furnace lining has an important influence on the heating process of the object. Because gas combustion is not like pulverized coal combustion, it can radiate energy through solid particles of pulverized coal, and it is not like fuel combustion to generate carbon black radiation energy. Among the main products of gas combustion, only the three atom gases such as CO2 and H2O have better radiation performance, and the radiation spectrum is not continuous. Therefore, how to strengthen the high temperature heat transfer process in the furnace is a problem that must be considered in the gas industrial furnace.

At present, some manufacturers use blackbody enhanced radiation heat transfer technology, that is, multi-functional furnace lining. This technology mainly heats these blackbody elements by the process of radiation and convection heat transfer through the flame, that is to say, let the inner lining of gas industrial furnace absorb the heat of high temperature flame through the process of radiation and convection heat transfer as much as possible, and then radiate heat transfer from these blackbody elements to the heated material, so as to indirectly improve the heating intensity of gas flame to the object.

Blackbody element is the key technology of multi-functional lining industrial furnace. The blackbody element obtains heat under the convection and radiation heat transfer of the gas flame, increases the temperature, and radiates energy to other directions of the furnace space, so that the heat transfer process in the furnace can be redistributed. The radiation intensity of blackbody components is related to its emissivity and temperature. However, if the emissivity of the common furnace lining is low and the heat of the gas flame cannot be effectively transferred to the heated object, and the convection heat transfer of the gas flame is not strengthened, the exhaust gas temperature will be relatively high, which will cause the loss of high temperature exhaust gas. From this point of view, the installation of blackbody elements on the furnace lining can effectively increase the heat absorption of the heated object. At present, a kind of blackbody element in the form of conical porous ceramic cavity can not only increase the heat transfer of the furnace lining, but also improve the blackness of the furnace lining, and strengthen the radiation heat transfer ability of the furnace lining to the object. It has been applied in relevant projects with good effect. In addition, the exhaust gas temperature of industrial furnace is generally above 200 ℃, and the water vapor in the flue gas is still overheated, and the latent heat of water vapor vaporization can not be applied. If the deep utilization of flue gas residual heat is carried out, that is, reducing the flue gas temperature to below 100 ℃, the latent heat of vaporization of water vapor in flue gas can be fully recovered, and the energy utilization efficiency can be increased by 10 percentage points. Under certain conditions, even the situation that the energy utilization efficiency is 100% higher (because the input energy is calculated according to the low heating value, the vaporization of water vapor in flue gas is not considered) Latent heat). However, low temperature corrosion is a problem that needs special attention at this time.

At present, the steel or process measures that can resist the low temperature corrosion have been developed, which can ensure that it will not rust in a maintenance period and affect the normal operation. If the economic value brought by the recovery of flue gas waste heat depends on the replacement and maintenance of the heat exchanger, the technology of deep utilization of flue gas waste heat can be popularized.