De-bottleneck final heaters on pasteurizers and eliminate nuisance flow diverts.
While legal pasteurizers are very common in food and dairy plants and come in a variety of configurations, this discussion will focus on pasteurizers that are integrated with an evaporator that immediately follows. An integrated pasteurizer is one where one or more of the pasteurizer heaters is dependent upon a heating medium that originates from the evaporator.
Operationally, in every start-up case, the pasteurizer must be charged with product and coupled with the evaporator smoothly and quickly to establish a continuous and stable process. To accomplish this, the pasteurizer heater(s) must be designed to easily reach and then maintain legal pasteurization temperature (165ºF). Failure to do so can result in a series of flow diverts, which interrupt a stable flow and feed temperature to the evaporator. In some cases, cycling can occur until forward flow can finally be maintained. Valuable production time and solids are usually lost.
What are the consequences of such frequent flow diversions during start-up? Here are a number of typical scenarios:
- Each flow divert causes an interruption of feed to the evaporator, which always disturbs the smooth ramping up of product concentration that occurs within the evaporator. Since evaporators are NOT permitted to run dry (no feed), water must be injected at the proper rate to replace the diverted flow. Therefore, each divert results in product dilution within the evaporator, and each divert can easily extend the time to achieve target concentration by 5-10 minutes. At the same time, the quantity of low solids concentrate that exits the evaporator increases and must be dealt with. This can be quite problematic if the evaporator is feeding a spray dryer.
- A single flow divert event can easily lead to a series of divert events, due to the instability that is created within the evaporator. When the heat flow from the evaporator to the pasteurizer heaters is interrupted frequently, stability can be very difficult to achieve. The design of the heaters, especially the final heater, must be robust enough to overcome these unstable conditions.
- Some facilities also lack sufficient hot water to inject into the evaporator for the duration of one or more sequential flow divert events. In this case, the instabilities can be amplified and take significantly longer to resolve. An hour of production and significant solids losses are typically the result.
- One extreme consequence of insufficient water to feed the evaporator is that the evaporator is starved of feed, runs mostly dry for a time, and tubes become plugged. This will result in a total stoppage of production, followed by at least (4) hours to CIP.
- A still more extreme scenario is when cold water is injected instead of hot water. When this occurs, extreme thermal shock can cause the evaporator tubes to rupture free from the tube sheet. This amounts to serious equipment damage that can be costly and time consuming to repair.
Do any of these situations sound familiar? If so, there are solutions. The start-up procedure can sometimes be modified and better automated to avoid flow diversion events, but often this is not enough. In many cases, the decisive step to take is to upgrade one or more of the heaters, often the final heater. When the heaters are capable of doing more work, in one manner or another, flow diversion events can be eliminated entirely.
Think about discussing your pasteurizer problem with Caloris, and let’s develop a plan together that can resolve these pasteurizer problems once and for all.
Some of the issues described above are also characteristic of stand-alone pasteurizers—those whose heat source is totally independent of an evaporator. Should problems as described be occurring with your stand-alone pasteurizer, Caloris can apply many of the same solutions. Feel free to call and discuss the situation.
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