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The gas is generally not stored on-site, but rather supplied through pipe networks. , 2005). For liquid fuels the control is slightly more complex. In most cases the liquid fuel is stored in tanks on-site, and from there it is pumped to the burner. In order to achieve satisfactory operation from the burner the fuel needs to be supplied at a certain pressure. The fuel pumps must therefore be controlled in combination with valves to maintain this fuel pressure. Depending on the type of fuel used, some additional monitoring may be needed.

For example, boilers with small portions of fuel burning at a time where the reaction therefore is fast, such as a fluidized bed, will require faster control and updates as often as each minute. , 2002). 1. Indirect Method The indirect method is based on the assumption of a relation between moisture in fuel and moisture in flue gases. By analyzing the flue gases, moisture content in fuel can be calculated. Moisture in flue gases originates from mainly three sources; hydrogen in the fuel forming water during combustion, moisture in the fuel, and humidity in the inlet air.

Measurement instruments for TDS are based on determining the conductivity of the boiler water. Pure water is a poor conductor while water with high levels of TDS conducts electricity well. The electrical signal is then interpreted into concentration and parts per million. , 2010a). Boiler water can be discharged periodically or continuously. All systems are designed for periodical blowdown where water is taken from the bottom of the boiler to remove sludge and settled particles. In continuous blowdown systems, water is discharged from the surface at a certain rate, manually or automatically determined.