I. Introduction Heat pipe is a kind of heat transfer element with extremely high thermal conductivity. The heat pipe heat exchanger consisting of heat pipe has the advantages of high heat transfer efficiency, compact structure and small fluid resistance. At present, it has been widely used in metallurgy, chemical industry, oil refining, boiler, ceramics, textile, machinery and other industries, and has achieved remarkable economic benefits.
Second, heat pipe type hot blast stove The hot blast stove is a device that burns fuel, heats air, and produces hot air. With the development of heat pipe technology, heat pipes are also being used as heat transfer elements in hot air furnaces. The heat pipe type hot blast stove has the following advantages compared with other types of hot blast stoves:
(1) The length ratio of the cooling section and the heating section, the fin density and the two sections of heat transfer area can be artificially adjusted to enhance the heat exchange at the cooling end to lower the wall temperature;
(2) Heat pipes of different structures and different working fluids can be used in the high temperature zone and the low temperature zone; avoiding the use of expensive materials as a whole for adapting to high temperatures;
(3) The pipe is detachable and easy to install; the heat pipe can be freely extended at both ends, and there is no thermal expansion or thermal stress problem;
(4) The flue gas side is the heat exchange outside the pipe, so the ash is easier to clean;
(5) Due to the use of finned tubes to enhance heat transfer, the entire equipment structure is relatively compact.
Third, spray drying The thermal efficiency of spray drying equipment can generally be expressed as:
Total efficiency η: η = (t1-t2) / (t1-t0) × 100%
Where: t1-t2——temperature difference of hot air during drying (ie inlet air temperature - exhaust air temperature) [°C]
T0——atmospheric temperature [°C]
As can be seen from the above formula, increasing the temperature of the hot air is the key to improving the thermal efficiency. Therefore, in actual operation, under the premise of not affecting the quality of the material to be dried, it is of great significance to save energy by increasing the hot air inlet temperature and reducing the exhaust air temperature as much as possible.
For the spray drying of silica, if the heat and mass of the material are used for mass transfer heat exchange, the hot air at 550 °C will not affect the product quality. Therefore, in order to improve the drying heat efficiency and reduce the operating cost of the silica, the inlet temperature of the hot air should be increased as much as possible. However, if an ordinary hot air furnace is used, it is difficult to generate hot air of 400 ° C or higher.
Fourth, application According to different temperature zones, hot-air stoves use high-temperature heat pipes, medium-temperature heat pipes and ordinary water-carbon steel heat pipes. The hot air temperature of the hot air stove can reach 550 °C. The basic parameters of the hot blast stove are as follows:
Heat load: 880kW (750,000 kcal / hour)
Flue gas inlet temperature: 850 ° C
Flue gas outlet temperature: 180 ° C
Hot air outlet temperature: 550 ° C
Fuel: coal
The high-temperature heat pipe hot blast stove has been used in a factory in Fujian, the hot air is clean, and all the indicators have met the design requirements, which fully meets the production process needs of the plant. The original project design scale is 2,000 tons per year. After using this equipment, the annual output can reach 3,000 tons due to the breakthrough of the production bottleneck. Compared with the traditional hot blast stove, the hot air temperature is increased from 350 °C to 550 °C; the drying efficiency is from 60% increased to 81%. The comprehensive annual economic benefit reached 700,000 yuan.
V. Summary of the heat pipe hot blast stove as a new type of hot blast stove, it can obtain clean hot air above 500 °C, can meet the needs of various hot air equipment; and the smoke exhaust gas temperature is low, so the heat efficiency is high and the fuel is saved. An energy efficient hot air device. It is not only suitable for spray drying of silica, but also suitable for drying many foods, pigments and other chemical products.