Horizontal Shell-and-Tube Jet Heat Exchanger

The KRH series hot air furnaces consist of an automatically fed grate combined with a new type of heat exchanger. This hot air furnace features a separate structure from the heat exchanger, utilizing jet flow heat exchange for high temperatures and agitation inserts for medium and low temperatures. This design ensures complete combustion and efficient heat transfer. The clean air produced is suitable for drying and processing materials such as chemicals, grains, foodstuffs, medicinal herbs, tea, paint, textiles, chromic acid, silica, dairy products, artificial raw materials, and bioproducts.

We offer stainless steel high-temperature, medium-temperature, and low-temperature shell-and-tube heat exchangers, as well as custom manufacturing services. Our high-temperature models utilize 310S stainless steel seamless tubes with built-in jet tubes. Our medium- and low-temperature models use 304 stainless steel seamless tubes with built-in spiral inserts, also known as agitation fins.

  A heat pipe is a heat transfer component with extremely high thermal conductivity. Heat exchangers composed of heat pipes offer advantages such as high heat transfer efficiency, compact design, and low fluid resistance. They are currently widely used in industries such as metallurgy, chemical engineering, oil refining, boilers, ceramics, light industry and textiles, and machinery, where they have yielded significant economic benefits.

II. Heat Pipe Hot Air Furnace  

A hot-air furnace is a device that burns fuel to heat air and produce hot air. With the advancement of heat pipe technology, heat pipes are now being used as heat transfer elements in hot-air furnaces. Compared to other types of hot-air furnaces, heat pipe-type hot-air furnaces offer the following advantages:

(1) The ratio of the cooling section to the heating section, the fin density, and the heat transfer areas of both sections can be adjusted to enhance heat exchange in the cooling section and reduce wall temperatures;

(2) Heat pipes with different structures and working fluids can be used in the high-temperature and low-temperature zones, respectively; this avoids the need to use expensive materials throughout the entire system solely to accommodate high temperatures;

(3) The tubes are removable, facilitating installation; both ends of the heat pipes can expand freely, eliminating issues related to thermal expansion and thermal stress;

(4) Heat exchange on the flue gas side occurs on the exterior of the tubes, making ash buildup easier to clean;

(5) The use of finned tubes to enhance heat transfer results in a more compact overall equipment design.

III. Spray Drying 

The thermal efficiency of spray drying equipment can generally be expressed as follows:

Overall efficiency η: η = (t1 – t2) / (t1 – t0) × 100%

Where: t1 – t2 — the temperature difference of the hot air during the drying process (i.e., inlet temperature – outlet temperature) [°C]

t0 — ambient temperature [°C]

As can be seen from the above equation, increasing the temperature of the hot air is key to improving thermal efficiency. Therefore, in actual operation, provided that the quality of the material being dried is not compromised, maximizing the hot air inlet temperature and minimizing the exhaust air temperature are of great significance for energy conservation.

In the case of silica spray drying, if mass transfer and heat exchange are conducted with hot air and the material flowing in the same direction, even hot air at 550°C will not affect product quality. Therefore, to improve drying thermal efficiency and reduce the operating costs of silica production, the inlet temperature of the hot air should be increased as much as possible; however, it is difficult to generate hot air above 400°C using a conventional hot air furnace. 

IV. Applications

The hot air furnace utilizes high-temperature heat pipes, medium-temperature heat pipes, and standard water-carbon steel heat pipes in different temperature zones. This design enables the hot air temperature to reach 550°C. The basic parameters of this hot air furnace are as follows:

Thermal load: 880 kW (750,000 kcal/h)

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 air furnace has been in operation at a factory in Fujian to date. The hot air is clean, and all performance indicators have met design requirements, fully satisfying the production process needs of the factory. The original project was designed for an annual production capacity of 2,000 tons. Since the installation of this equipment, the production “bottleneck” has been eliminated, enabling an annual output of 3,000 tons. Compared to traditional hot air furnaces, the hot air temperature has increased from 350°C to 550°C, and drying efficiency has improved from 60% to 81%. The comprehensive annual economic benefit amounts to 700,000 yuan.

V. Conclusion 

As a new type of hot-air furnace, the heat pipe hot-air furnace can generate clean hot air at temperatures exceeding 500°C, meeting the needs of various hot-air applications. Furthermore, due to its low flue gas exhaust temperature, it offers high thermal efficiency and fuel savings, making it a highly efficient and energy-saving hot-air system. It is not only suitable for the spray drying of silica but is also ideal for drying a wide range of food products, pigments, and other chemical products.