PROCESS TANKS FOR INDUSTRY

Heat exchangers on process tanks are used in various technological processes – including the thermal treatment of stored or mixed products. These types of tanks are used in the food, chemical, petrochemical, and pharmaceutical industries.

These tank heat exchangers are used for heating, cooling, and temperature control in technological processes such as pasteurization, fermentation, mash liquefaction, cooking, chemical synthesis, and tempering. FME Food Machinery Europe Sp. z o.o. has been operating in Poland since 2007 as a manufacturer of machinery, equipment, and process lines used in the food industry – fruit and vegetable processing.

Automation of the production of coil heat exchangers on process tanks

1. Application of heat exchangers in tanks

Heat exchangers on process tanks are used in various technological processes – including the thermal treatment of stored or mixed products. These types of tanks are used in the food, chemical, petrochemical, and pharmaceutical industries. These tank heat exchangers are used for heating, cooling, and temperature control in technological processes such as pasteurization, fermentation, mash liquefaction, cooking, chemical synthesis, and tempering. FME Food Machinery Europe Sp. z o.o. has been operating in Poland since 2007 as a manufacturer of machinery, equipment, and process lines used in the food industry, including fruit and vegetable processing.

Continuous improvement and enhancement of the quality of our products and services requires investment in new technological solutions to meet customer expectations, expand into new markets, and gain a competitive advantage. Therefore, the company decided to improve the production of process tanks used in the food industry, including in process lines for the production of beverages, juices, ketchup, fruit purees, jams, confectionery fillings, fruit mousses, chocolate, and syrups. Process tanks are among the most commonly used devices in food production, and the food industry demonstrates a constant demand for innovative product and technological solutions. Due to the nature of the process, tanks can serve as storage, buffers, or be used for thermal technological processes. The need to use a tank for mixing, heating, cooling, maintaining temperature, or storing a medium occurs at various stages of the technological process. Therefore, process tanks are an essential element of most production lines in the food industry.

2. Computer simulation of coil components on a process tank

Thanks to the use of SolidWorks CAD software in the design office, a series of computer simulations were performed to shorten the time required to develop the optimal cross-section of the shaped coil and reduce its manufacturing costs.

The assumptions used to conduct computer simulations to obtain the correct coil profile included: resistance to pressure of at least 6 bar, suitability for plastic shaping (rolling and winding onto the tank shell), low sensitivity to pressure and temperature changes, high resistance to boiler scale formation, low flow resistance of the heating and cooling medium, high corrosion resistance, and low weight. These computer simulations resulted in the optimal coil cross-section.

3. Research and Development, In-House Research

This cross-section was created using a press brake bending technique and then manually TIG welded to a flat sheet. The prepared element was subjected to a hydrostatic test, during which deformation and pressure resistance were assessed. Our own research demonstrated that the designed coil shape withstood operating pressure at an ambient temperature of 140 bar without failure. The test pressure was limited by the capabilities of the hydrostatic testing device that had been adopted and used to conduct tests under real-world pressure resistance conditions. A 1200mm-long coil was manufactured for the tests.

At the conclusion of the research project, the design and technological solutions developed during the R&D work were tested under real-world conditions. Therefore, an automated technological station was developed and designed for the production of a series of process tanks.

4. Design of an automated station for the production of heat exchangers in the form of a coil on the shells of process tanks.

The main assumption of this project was that in a single technological cycle, the coil is formed, rolled, and simultaneously welded to the outer shell.

The main components of this station are: a column-and-boom, on whose arm is mounted a welding unit containing two TIG welding torches with wire feeding to the weld pool; a roll-and-roll machine for shaping channels, attached to the column-and-boom; and an actuator with adjustable pressure force. The actuator has a pressure roller attached to the end of the piston rod, which is responsible for rolling the coil channel to the outer surface of the tank's shell of a given diameter. This allows the shape of the coil channel to automatically adapt to the outer diameter of the tank. The coil profile is formed using a rolling mill. The welding station's roll-and-roll machine contains five pairs of rolling rolls, each driven by a gear motor. The desired shape of the coil profile is achieved by passing the sandblaster through successive pairs of rolls, which increase plastic deformation, resulting in the correct channel geometry. The welding station's column-and-boom arm is pivotally mounted on a carriage mounted on the first track via a slewing bearing. The column-and-boom rotation is achieved via a gear transmission and a servo drive. The second track carries an active roller support and a passive roller support, supporting a tank with diameters ranging from 1200 to 3200 mm. The active roller support forces the tank to rotate depending on the welding speed. The welding station is equipped with a tilt-and-rotate positioner for creating coils on tanks with diameters ranging from 780 to 1200 mm. A gas dispenser is mounted on the rolling mill side to protect the root of the coil profile and also contains a ground element that allows for closing the welding circuit. The flat bar in the coiled coil is mounted in front of the rolling mill. Welding is performed using the GTAW method in an inert gas shield, using nitrogen-forming gas to protect the weld root within the coil profile at the welding point. The tank is set in rotation, and the torch positions are changed along with the column-and-boom carriage and the rolling mill, which move in a straight line synchronized with the tank's rotation. Two devices with a maximum welding current of 500A, manufactured by Closs Polska, are installed as power sources for the GTAW method. These devices maintain a constant arc length between the weld pool and the torch, regardless of the precision of the tank shell. This distance depends on the voltage during arcing. The longer the arc, the higher the voltage. This signal is sent to the PLC, which, through an appropriate algorithm, transmits a control signal to the servo drive, which forces the torch to move and thus maintains the desired arc length. During the fabrication of the coil on the outer surface of the tank shell, the PLC controller must synchronize the tank's rotational speed with the linear speed of the column-and-boom carriage, the column-and-boom angle, the channel-forming speed, the channel-feeding speed onto the tank shell, and the burner power.

5. Tanks with heat exchangers on the outer surface of the shell manufactured on a robotic station.

Heat exchangers manufactured on this station allow for high repeatability and high quality of entire process units, while also eliminating or minimizing the unfavorable phenomena that occur with manual welding. The optimal geometric dimensions of the welded coil allow it to be supplied with high or low pressure. This method of fabricating the heat exchanger on the process tank shell allows for maintaining an intact internal surface of the process tank below a roughness of Ra 0.8 um. This solution allows for use as a semi-finished product (flat bar) to fabricate a uniform coil up to 300 meters long. The use of optimal welding parameters, depending on the tank shell thickness, coil profile thickness, and welding speed, allows for the production of repeatable welded joints from AISI 316L and AISI 304 materials with high corrosion resistance, a small heat-affected zone, higher impact strength, and the ability to use higher pressures for heating or cooling media. Furthermore, the welded coil on the outer surface of the tank shell strengthens the structure because it is made of a single piece of material that is not overheated and has low welding distortion. Therefore, thinner sheets can be used for the shell, increasing the thermal conductivity between the heating or cooling medium and the fluid inside the tank.

The technological station constructed in this manner has been submitted for patent protection no. P433821 on May 8, 2020.

A series of tank types with a coil jacket welded on both sides to the tank side jacket at an automated station

The values ​​provided in the table may vary depending on the tank design.

The above data applies to a coil stroke of 150 mm, which for technological reasons is the minimum stroke.

It is possible to manufacture a coil with a shell stroke greater than 150 mm, as well as with a thicker insulation of 100 or 150 mm.

It is possible to install a coil at the bottom of the tank, but only if the bottom end is conical. This design solution is priced individually.
Other tank sizes, designs with agitators, nozzle layouts, and other requirements are available and priced individually.