Project Background
Our customer is a leading manufacturer of dairy products including nonfat dry milk and skim milk powders. A key step in the milk drying process is to pre-heat the milk prior to entering the dryer using various types of heat exchangers. The type of heat exchanger our customer used to pre-heat their milk was a triple tube which required frequent servicing. Wear items, such as gaskets and seals, must be replaced to keep the heating medium from entering the product side of the tubes. When the triple tube is taken out of service for maintenance the plant must reduce production as this piece of equipment is critical to the milk drying process. The long and labor-intensive process of servicing the triple tube heat exchanger results in significant plant downtime, thus, a significant loss in product output.
The milk pre-heat temperature directly affected the milk dryer capacity, thus, plant product output – the higher the milk pre-heat temperature, the greater the plant product output. The triple tube milk pre-heat output temperature was limited by the hydronic warm water circulation system maximum operating temperature. When operating the warm water system at maximum temperature, the plant product output was at full capacity. The temperature limitations of the hydronic warm water circulation system were ultimately determining the plant’s product output capabilities.
Other facilities owned and operated by our client had been using a multi-pass concentrate pre-heater in place of the triple tube with great results as it could meet their production needs with little to any maintenance downtime. Our customer partnered with Placer Process Systems to replace the existing triple tube pre-heater with multi-pass concentrate pre-heater.
Project Hurdles
Due to the milk pre-heater’s direct impact on plant production, the timeline to perform the pre-heater replacement was of at most importance. Simply removing the existing triple tube, installing the replacement multi-pass concentrate heater, installing new utilities lines and components, and re-connecting process lines in series would result in too much production downtime and product loss for the plant to bear.
Our customer also needed to increase the plant’s production capacity which meant the milk pre-heat temperature would need to be increased. The typical milk pre-heat heating mediums are water, not steam. The existing hydronic warm water system was already operating at its maximum temperature while introducing steam in a conventional throttled manner would scald the milk due to the temperature being too high. The replacement multi-pass concentrate pre-heater would need to pre-heat the milk to a higher temperature using a medium that would be higher in temperature than the existing warm water system but not scald the milk.
The existing footprint must also be maintained as to not take away from operator access to neighboring equipment.
With any type of equipment that is subjected to severe increases in temperature, thermal expansion should always be a taken into consideration to extend the life of the equipment. The replacement multi-pass concentrate pre-heater was very large and was designed to be anchored and fixed to a support structure. By doing so, the body of the multi-pass concentrate pre-heater would not be allowed to thermally expand as steam is applied to the shell which could impose great stress on the support structure and welds.
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Solution
Placer Process Systems needed to come up with ways to reduce the plant downtime by performing portions of the multi-pass concentrate pre-heater installation before the triple tube would be taken out of service. The most effective solution was to skid mount the multi-pass concentrate pre-heater on a stainless steel frame because the frame would allow the utility and auxiliary equipment to be mounted and plumbed prior to performing the swap. This greatly reduced the amount of time required to complete the installation once the multi-pass concentrate pre-heater was set into its final position.
Another way downtime was reduced was by designing the frame so that the locations of the frame and triple tube mounting feet were in identical locations. The intent was to minimize, if not, eliminate the need to rework the floor with grouting and floor coating because the existing pedestals could be reused. This not only saved downtime but project cost as well.
The multi-pass concentrate pre-heater uses steam under vacuum as the milk heating medium. This met the requirement of using a heating medium that is higher in temperature than the existing hydronic warm water circulation system. However, this also resolved the typical issue of steam scalding the milk because the temperature of steam under vacuum is only slightly higher than the temperature of water near boiling under atmospheric pressure.
To account for thermal expansion, instead of following the traditional method of fixing the opposite ended multi-pass concentrate pre-heater feet to the frame, Placer Process Systems designed a slide base positioned under one of the mounting feet. By fixing one foot and allowing the other to slide the multi-pass concentrate pre-heater would be allowed thermally expand without restraint. This eliminated the possibility of unwanted stresses that could have reduced the pre-heater’s life. The slide base was designed to prevent horizontal pivoting by incorporating slide guides around the pre-heater feet to only allow the multi-pass concentrate pre-heater to move in the axial direction.
Results
The concept of skid mounting the multi-pass concentrate pre-heater along with the auxiliary equipment and utility components reduced the original proposed installation timeline by days. This kept the plant downtime to an acceptable limit and as a result minimized production loss. And by using steam under vacuum as the heating medium, the multi-pass concentrate pre-heater’s milk pre-heat output temperature was higher than its predecessor. The direct result of increasing the milk pre-heat temperature was an increase in the air dryer capacity. By replacing the triple tube pre-heater with a multi-pass concentrate pre-heater, our customer was able to reduce scheduled shutdowns for pre-heater maintenance, reduce the shutdown duration, as well as increase the plant’s product output capabilities.