The mixture controller can be used in a biogas plants. Often, the available biogas flow rate is not sufficient to meet the load requirement for the burner capacity.

If this is not the case, the biogas would be the fuel to be combusted with priority in simultaneous firing to achieve the desired output.

In most cases, the available biogas flow rate is not constant. The biogas is produced via biogas reactors, from which the biogas is compressed via a compressor and buffered in a biogas tank. As a rule, the biogas pressure is approx. 200 mbar.

To keep this pressure constant in the biogas tank, a pressure preservation controller (mixing controller) must be used. The actuating signal of the load controller is transmitted to the FSC, which controls the electric compound and thus the fuel control valves. With increasing load requirement, the fuel control valves will be opened to release an increased gas flow rate for combustion.

In a biogas plat, the biogas is to be combusted with priority. For this reason, first only the biogas control valve will be opened while the natural gas control valve remains in low load position. If the biogas pressure drops, the pressure preservation controller (mixture controller) will reduce the biogas flow rate by closing the biogas control valve. Thus, the pressure in the biogas tank will be built up again. At the same time, the natural gas control valve will be opened to compensate for the missing fuel requirement.

You must dynamically limit the actuating signal of the mixture controller if the efficiency of the primary fuel (biogas) does not cover the full burner capacity rating

For additional explanations, see the "System manual: Training: Simultaneous firing".