In the beer industry, the manufacturing material of fermenters has gradually shifted from traditional carbon steel to stainless steel. Stainless steel fermenters not only better meet process requirements in terms of fermentation technology, but also show irreplaceable advantages in comprehensive investment cost and later maintenance.

1.Material and refrigeration of carbon steel fermenters

1.1Material

Traditional carbon steel fermenters are generally made of ( ) material. After the tank body is fabricated, it is necessary to grind the inner surface of the tank, sandblast to remove rust, and apply internal anti-corrosion coating ( ). These operations all need to be carried out inside the tank; the working conditions are harsh, which is not conducive to workers’ safety protection and to tracking quality inspection of the tank. After spraying the internal anti-corrosion coating, the roughness of the inner wall is limited, and it is difficult to meet the aseptic environment required for current draft beer brewing. The service life of the internal anti-corrosion coating is short, generally about ( ) years, and after it falls off it is not easy to discover in time, affecting beer quality. Each time the internal anti-corrosion coating is maintained and replaced, it is time-consuming and laborious, affecting the normal production schedule of beer.

1.2Refrigeration

Due to material limitations, traditional carbon steel beer fermenters mostly use alcohol-water as the refrigerant, and are cooled through a half-pipe jacket. This not only increases investment and wastes energy, but also has the potential danger that the refrigerant may leak into the tank and contaminate the beer liquid. Alcohol-water cooling works as follows: liquid ammonia absorbs heat and evaporates in the evaporator, cooling the alcohol-water in the alcohol-water pool. The alcohol-water is pumped into the fermenter jacket to cool the fermentation liquid in the tank. After absorbing the heat inside the tank, the alcohol-water temperature rises and returns to the alcohol-water pool to be cooled again. After the liquid ammonia evaporates by absorbing heat in the evaporator, it becomes gaseous ammonia; after gas-liquid separation, the gaseous ammonia is sucked into the compressor for compression, then condensed into liquid ammonia by the condenser and enters the liquid ammonia storage tank. The liquid ammonia in the storage tank enters the evaporator again to absorb heat and evaporate, thus circulating. This refrigeration method requires large investment and has serious energy loss. The fabrication of the half-pipe jacket is generally either single-helix upward winding or multi-helix parallel upward winding; no matter which method is used, it is unavoidable that the half-pipe covers the circumferential seams and longitudinal seams of the cylinder. In fabrication, radiographic inspection is required for the welds covered by the jacket, increasing manufacturing cost and construction period. Even so, weld leakage may still occur. Once leakage happens, alcohol-water will directly seep into the fermenter through the weld seams and contaminate the beer liquid.

2.Material and refrigeration of stainless steel fermenters

2.1Material

By comparison, stainless steel fermenters have obvious advantages. Stainless steel fermenters use ( ) material. The inner surface is automatically mechanically polished; the maximum roughness can reach ( ), and the polishing texture is consistent with the direction of CIP water flow, truly achieving “cleaning without residue.” Under normal use, there is basically no need to enter the tank to maintain the tank wall; the service life of stainless steel fermenters can reach ( ) years. The polishing, fit-up, and installation work of the tank are all completed at low altitude; the workers’ operating environment is safe and is also conducive to quality control.

2.2Refrigeration

In terms of refrigeration, stainless steel fermenters have more choices. In addition to using the traditional manual argon-arc welded half-pipe alcohol-water cooling, they can also use the most advanced laser-welded, bulge-formed honeycomb jacket with direct liquid-ammonia cooling. The laser-welded bulge-formed honeycomb jacket is made by laminating two steel plates of different thicknesses. Laser welding is used to firmly weld the two plates together in a certain geometric pattern, and then water is filled between the two plates and pressurized so that the thin plate bulges in the non-welded areas into a convex arc shape. The heat exchange of liquid ammonia in the jacket is essentially the process of liquid ammonia absorbing heat, gasifying, boiling, and transferring heat. Boiling heat transfer is one of the most effective energy conversion methods in today’s thermodynamic processes; when liquid ammonia When it flows in the jacket, due to the change of channel cross-section width and the obstruction of the welded areas, the liquid in the cavity is very prone to turbulence, and the heat transfer performance is improved.

Compared with the alcohol-water cooling system, the ammonia cooling system eliminates the heat exchange cycle in which liquid ammonia is evaporated to cool alcohol-water and alcohol-water cools the beer liquid inside the fermenter, avoiding intermediate heat energy loss and achieving energy saving. At the same time, it also eliminates the ammonia evaporator, alcohol-water pool, alcohol-water and the loss caused by alcohol-water volatilization, saving investment and reducing floor space. In manufacturing, the laser-welded honeycomb jacket can be divided into segmented pieces. When the jacket is welded to the cylinder, the longitudinal and circumferential weld seams of the cylinder can be avoided. In this way, for the fermenter, the possibility that the refrigerant liquid ammonia seeps into the fermentation liquid in the tank through weld seams is eliminated, improving safety in use. In addition, the flaw-detection requirements for the cylinder’s longitudinal and circumferential weld seams are also reduced, thereby saving flaw-detection costs. Laser weld seams are narrow, the heat-affected zone is small, thermal stress is small, and welding deformation is small. Therefore, laser-welded honeycomb plates have extremely high strength and rigidity, and good quality. Test data prove that the burst pressure of the laser-welded honeycomb jacket is far higher than that of other welding-method jackets of the same plate thickness and the same structural dimensions. The entire laser-welded jacket is automatically welded indoors by a laser welding machine according to programs, and there is no situation like manual argon-arc welding being affected by weather, welder skill level, emotions, etc., which would affect weld quality. Fermenters using laser-welded jackets can be manufactured in segmented sections: the laser welding of the jacket portion of the cylinder is completed in the equipment manufacturing plant, shortening the on-site construction period and reducing requirements for the on-site construction site.

3.The greatest structural change between stainless steel fermenters and carbon steel fermenters

In fact, because of different materials, the greatest structural change between stainless steel fermenters and carbon steel fermenters is the jacket. The replacement of the two jacket forms (as shown in Fig. (1 ) and Fig. (2 )) is already a trend in the beer industry! Since the Qingdao Beer (Jinan) project in 2007, all new brewery projects of Qingdao Beer have, without exception, chosen the laser-welded honeycomb jacket.

Fig. (1 ) Stainless steel laser-welded honeycomb jacket

Fig. (2 ) Carbon steel half-pipe jacket

From the above, it is not difficult to see that stainless steel fermenters are superior to traditional carbon steel fermenters in process requirements, use, maintenance, and comprehensive investment, and are the inevitable trend of the development of beer fermenters.

References

Li, Xiaobin. “Application of Stainless Steel Beer Fermenters.” Beverage Industry, vol. 15, no. 9, 2012, pp. 38–39. doi:10.3969/j.issn.1007-7871.2012.09.010.