- Water level
- Boiler pressure
- Continuous total dissolved solids (TDS)
- Timed bottom blowdown
- Main steam warm-up
- Open communication
- Flexible user interface
Incorporating all the main boiler control elements, the 2704 is ideal as an integrated control solution for packaged boilers.
Optimized control performance provides for lower emissions, reducing energy costs and making for a cleaner environment. In particular, continuous control of the boiler TDS will vastly improve boiler efficiency.
A specialist input module makes the 2704 compatible with standard TDS probes making both retrofit and new installations easy to accomplish. The controller can also provide combustion fuel/air ratio control or cooperate with existing burner management control systems.
Total Dissolved Solids
As we take steam from a boiler and top it up with water, dissolved liquids tend to build up in the water. Eventually the level of dissolved solids will cause problems with the efficiency of the boiler. At high parts per million (PPM) levels, foaming on the water surface will occur and may “carry over” to the steam main. If this happens then the boiler may require a shutdown for steam system cleaning to remove contamination.
What is TDS?
The TDS measurement indicates the amount of solids dissolved in water. If measured in PPM (parts per million), the value directly indicates the mass of dissolved solid molecules in the fluid as a proportion of the total mass of the solution. The alternative measurement in mg/L (milligrams per liter) is equivalent – since a liter of water has the approximate mass of 1kg. The most reliable way of measuring TDS is to evaporate water from a unit volume of a solution and the weigh the solid residue (commonly referred to as TDR – total dry residue). Fortunately the solids dissolved in naturally occurring water are of the type which cause water ionization – and hence have a direct influence on its electrical conductivity. Measuring conductive properties makes it possible to estimate TDS.
To control TDS we use both a continuous control method and an intermittent method called “Bottom Blowdown”.
Systems normally maintain a TDS value of about 2500PPM. When the TDS is high the controller opens a valve to bleed water from the boiler with the effect of reducing the water level. The level controller compensates for this by introducing water with a low TDS value – therefore reducing the overall TDS.
TDS Function Block
The TDS function block converts the measured conductivity value, as measured by the TDS module in mS, to a temperature compensated TDS value in PPM(parts per million) or mS/cm at 25ºC. The block also allows a user to set a Probe Factor to cater for the relationship between the conductance measured with the probe and the specific conductance of the fluid. The TDS PV functions within a control loop that removes water from the boiler when it exceeds the loop setpoint. We call this method of control, Continuous Blowdown.
Timed Bottom Blowdown
Installing the 2704 as a TDS controller removes the need to manually lower the TDS but there is still a need to blowdown the sediment that forms at the bottom f the boiler. To minimize the energy loss, the controller restricts blowdown to a 3 second burst probably twice a day at a time selected by the boilerman.
A high integrity network connection between controllers ensures only one boiler is blowing down at any one time. The size of the receiving vessel usually requires this regulation.
Incorporating all the main boiler control elements, the 2704 provides a very cost effective control solution for packaged Fire- Tube Boilers.
Please call us at (800) 446-4316 or contact us here for more information on the Eurotherm 2704BC Controller.