Dry Cooler

How big must the dry cooler be?

The dimensioning of the dry cooler was the focus of this project. In addition, our customer wanted to clarify up to which ambient temperatures a dry cooler is sufficient at all and when a chiller must be used for support. This is to ensure that cooling can also take place sufficiently quickly in summer. If necessary, the use of a chiller also makes sense to reduce the size of the dry cooler and to enable a more flexible production process.

Cooling process with decreasing temperature difference

The design of dry coolers for batch processes is not trivial. As the temperature of the product drops during cooling, the temperature difference changes constantly and a steady-state analysis is not expedient. In addition, the ambient temperature can also change during longer cooling times.

In this case, the product has not been cooled directly, but is connected to the dry cooler via an intermediate circuit. Furthermore, additional cooling via chillers is optionally provided.

This results in the following simplified schematic of the plant:

Simulation of the cooling process

Even for this small problem, a dynamic simulation is useful due to the unsteady process conditions. Therefore, we have chosen the following procedure:

1. Mapping of the existing system in Modelica
2. Calibration of the model with measurement data
3. Simulation and evaluation of variants

The existing system can be completely mapped with standard components (e.g. pumps, tanks, heat exchangers) of the TIL library and can thus be set up quickly. A little more time is then required for the parameterization of the individual components so that the characteristics of the real components are correctly reproduced.

The most important step, however, is the calibration of the model with measurement data. This creates confidence in the model and enables quantitative statements to be made with the simulation. And this is an important prerequisite for the design of the cooling system.

In this project, we had time-resolved measurement data for various operating conditions at our disposal, so that an almost ideal calibration of the models was achieved.

With the calibrated model, we then carried out a simulation study to find the optimum design of the dry cooler. After the basic sizing of the dry cooler, numerous detailed questions arose in the discussion with the customer. Because even with this small system, there are many degrees of freedom that influence the performance of the cooling process:

• volume flow rate of the pumps
• temperature of product and environment
• size of the heat exchangers
• optional chiller

To avoid losing too much time in coordination processes, we simply made the simulation model available to the customer via our TLK Energy Apps web platform.

Our customer was then able to perform the detailed simulations themselves and present the results internally for discussion with the help of clear graphics.

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