Biogas appliances are domestic appliances. They serve a practical purpose. However, they are also relevant to the self-image of the housewife or master of the house. The biogas plant will be looked after better the higher the prestige value of the gas appliances. For this reason even simple, inexpensive gas appliances made in the village should be of appealing design. They must be not only cheap but also, and in particular, "modern".
Most households cook on two flames. Two-flame burners are preferred. The burners (Figure 41) should be set initially and then fixed. Efficiency will then remain at a high practical level.
In villages without electricity, lighting is a basic peed and a status symbol. However, biogas lamps have low efficiency. This means that they also get very trot.' If they hang directly below the roof, there is a fire risk. The mantles do not last long. It is important that the gas and air in a biogas lamp be thoroughly blended before the mixture reaches the gas mantle, and that the air space around the mantle be adequately warm.
Particular problems also arise with biogas-operated refrigerators. The composition of biogas varies substantially from day to day. The gas pressure fluctuates excessively with the amount of gas stored even in a floating-drum plant. Special' stable-burning jets are therefore needed - especially if the refrigerator is thermostatically controlled and the flame burns only when required. On every ignition there is a risk of the flame going out. Gas will then discharge without burning. The gas supply must therefore automatically be cut off if the flame goes out.
A gas appliance specialist must always be called in where biogas is to be used in refrigerators!
For use of biogas in engines see Figure 42.