Abstract:

This work reflects how a wall-mounted boiler has been re-used for heating and production of sanitary hot water with education purposes in the field of the engineering. The boiler has a fixed power of 8.7 kW heating and a variable power up to 20 kW for hot water production, using gaseous fuels as energy source.
As a main target was fixed the possibility of burning different gaseous fuels of the second family, specifically defined propane-air according to the percentages between the propane and the air (usually 57% propane / 43% air). The installation will allow to determine the calorific capacity and the Wobbe index for the different miscellanies. It will also allow to define the correspondent interchangeability diagram.
The design of the installation needed certain portability and it measures pressures and temperatures in different points. So the load losses of the different circuits could be analyzed.
For that, there was constructed a framework where was installed the thermal generator (boiler), the heat sink team (fan-coil), the air compressor and the gas cylinder, as well as the circuits of air, gas and water. The installation was also provided with diverse manometers, probes of temperature, flowmeters for the different fluids, and another equipment like valves of step and of safety, electrovalves, counters, etc.
The use of the compressor is to provide air to the necessary pressure so that the miscellany is realized with the propane, obtaining a gaseous fuel substitute of the natural gas to the pressure of 22 mbar.
The operation of the installation is based in feeding the boiler with propane air. For that, propane is given from the gas cylinder up to the mixer, where it is joined with the air produced in the compressor to the same pressure. The gas flow is controlled not only by the weighing of the gas cylinder in precision scales of 10g but by the corresponding flowmeter, and the air caudal is passed through its respective flowmeter. When the propane air is obtained it goes through the reducing valve and the gas counters where it gets across the burners in the boiler.
On the other hand, the installation is prepared to remove the heat produced in the fan-coil, where the useful energy is obtained according to the water flow and the temperatures and pressures of entry and exit of the circuit of heating. The installation has also the necessary connections to be connected to the water-supply system.
The students will have to identify the different elements and circuits of the installation, and by means of an exhaust gas analyser (which they will connect in an access into the exhaust duct of the flue gases) they will be able to estimate the efficiency of the boiler. When they get the composition of the propane and note down the suitable information, they will be able to represent an interchangeability diagram according to the different compositions of the propane air.

Keywords:

Boiler, propane-air, interchangeability.