Level control and heat transfer rig

Paul Boughton

The student training systems supplied to CNA-Q are air or liquid flow loops from standard Feedback training designs, but in general combine two or three separate process streams so that these can interact.

Further, the instrumentation installed is duplicated, in the sense that several devices perform similar functions at different points in the loop, to allow different modes of control.

For example, on one rig, the main process trainer uses water and air as the process fluids, allowing for three process loops that can be either individually controlled or operated as a multi-loop control system.

The primary loop heats the water in a small boiler which is then pumped through a heat exchanger. Temperatures on either side of the heat exchanger are monitored using Rosemount 3144 and 3244 transmitters, the flow rate is measured using a turbine flow transmitter and displayed using variable area flow gauge. The flow rate is controlled using a Fisher servo valve. The secondary water loop consists of a sump tank, pump, heat exchanger, Fisher control valve, forced air cooler and Rosemount 3051 DP cell round an orifice assembly. Water can either be returned directly to the sump tank or fed into the central Perspex storage tank fitted with level measurement by either capacitive sensor or a Rosemount 3051 pressure transmitter.

Temperatures are measured around the heat exchanger and at the output of the force air cooler using Rosemount 3144 transmitters. A third loop is provided using compressed air. This consists of two Fisher valves driven by DVC6000 valve controllers, with pressures being monitored by Rosemount transmitters. Flow rates are again measured using DP orifice gauges. Control of pressure and flow systems can be established. Interaction between the air, secondary flow and temperature processes are possible to replicate the types of system present in the natural gas plant common in Qatar. Control schemes can be established for this system based on the temperature differentials, the level in the storage tank, the flow rates measured, or similar. The training system allows the instructor to open bypass routes and faults to introduce anomalies in the process.

Most of the signals used on this rig are 4-20mA, although the turbines produce a pulse output, which is configured into 4-20 using an interface transmitter.

A typical student task set might be to implement a design system to control the flow in the secondary loop to the maximum level possible consistent with achieving a certain exit temperature range from the heat exchanger, while keeping the storage tank level below a certain value. 

Recent Issues