PipeNet-Cooling Water System Including a Controller 2

Introduction:

PIPENET shows how to reduce and control severe pressure oscillations which can sometimes be caused by a pump trip. When a pump trips it acts somewhat like a valve closing. This can create vacuum pressure downstream of the pump which subsequently leads to pressure oscillations.

PIPENET is used to model a cooling water system in this example. Cooling water systems are increasingly constructed using GRP pipes. This is mainly because GRP is less susceptible to corrosion and is cheaper. However, in order to harness these highly desirable qualities, when a cooling water system is built using GRP material one has to pay more attention to the design aspects. This is because they generally have to operate within a relatively narrow pressure range, and pressure oscillations should be minimised.

GRP pipes in the following cooling water network may work under vacuum conditions after pump trip. The GRP pipes may leak, or even collapse, because GRP pipe may be able to withstand limited negative pressure. Furthermore, it is important to minimise pressure oscillations. Pipe fittings are attached to pipes by the use adhesives rather than welding. Severe pressure oscillations can have the effect of causing relative movement between the pipe material and the fitting, ultimately causing them to become detached.

PIPENET Transient module is used to compare two alternative ways of solving the difficulties caused by the pump trip. The first one uses vacuum breakers, and the second uses a fly wheel attached to the pump rotor. The moment of inertia of the flywheel is the main factor of interest. PIPENET shows the effect of the moment of inertia of the flywheel. PIPENET also shows how to determine the sizes of the vacuum breakers, if this approach is taken to solve the problem.

One key aspect of the model is the following. In the usual pump performance curve supplied by manufacturers the downstream pressure is higher than the upstream pressure. However, when a pump trips the downstream pressure is lower than the upstream pressure. PIPENET provides the turbo-pump to model such situations, and this model must be used in this simulation.

The system generally has to operate within a relatively narrow pressure range, and pressure oscillations should be avoided if possible.

In this training example, we focus on modelling the pump trip scenario. We consider two alternative ways of solving the difficulties caused by the pump trip scenario. The first one uses vacuum breakers, and the second uses a flywheel attached to the pump impeller shaft. We also see how to size the vacuum breakers, if this approach is taken resolve the problem.

As can be seen from the following schematic of the network, the pump speed is controlled by a pressure control system and the valve position is controlled by a flow control system.

2. Input Data:

2.1. Initialisation Data:

Units:

Fluid Properties:

Pipe Types

The pipe schedules must be added to the built-in pipe schedules by entering them into the Library as shown in section 2.2. below before they can be selected here.

2.2. Library Data:

This should be input before the pipe type is selected in section 2.1.

Pipe Schedule Data:

CS flake line 1

GRP 1

Turbo Pump Data:

3. Network Data:

Short Pipes:

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