5.1.1 General system layout
5.1.2 The gasifier
5.1.4 Impingement separator
5.1.5 Glass fibre cloth filter
5.1.7 Engine and alternator
5.1.8 Start-up fan and flare
5.1.9 Safety devices
A schematic flow diagram for the power plant is shown in Figure 5.1.
The rated power output is 32 kW.
The gasifier is of the down-draught type with five air entrance openings. The throat diameter is approximately 15 cm, and the general dimensioning of the unit is in accordance with the design rules given in Chapter 2.
The throat is made from refractory cement. The inner side of the bunker is air-lined with this material. The hand-operated grate is positioned approximately 20 cm below the smallest cross-sectional area of the throat.
The gasifier is equipped with a double-valve hand operated filling sluice. '
Product gas exchanges heat with incoming air before it is passed on to the gas cleaning section.
Figure 5.1 Flow diagram for producer gas power plant at the Giriulla mill
The gasifier is equipped with an acoustic fuel level indicator which gives an alarm at the time refuelling is required.
Gasifier outlet temperatures as well as the pressure drop over the "throat" of the unit can be measured. Average values obtained with the different types of fuels tested are given in Table 5.1.
Coarse particles are separated from the gas stream in a high efficiency cyclone separator. Entrained ashes from the gasifier are collected in an ash bin which can be opened at the bottom for regular cleaning.
Intermediate size particles and most of the fines are removed from the gasifier in an impingement separator of special design. This separator is insulated so as to avoid condensation of vapours and to allow passage of hot gas (above 150°C) to the glass fibre cloth filter.
To guard the engine against any solid material, the product gas is passed through a glass fibre cloth filter, which removes any solids that have slipped through the previous filter sections.
In order to maintain the temperature above the dew-point of the gas and to avoid condensation (approximately 80°C) this filter is also insulated with rockwool and an aluminium lining.
Both the impingement separator and glass fibre cloth filter are equipped with water gauge manometers in order to permit the continuous monitoring of pressure drop caused by fouling of the filtering devices.
Originally, the glass fibre cloth filter was equipped with a safety condensate outlet. In Giriulla it was found that such a device was unnecessary. Because some water was condensing in the connection pipe between cooler (see below) and engine air inlet manifold, the drain vessel was removed from the filter box and put in the connection pipe, where it worked better.
The cooling section consists of a tubular heat exchanger. Condensate can be tapped from the cooler by means of two drain vessels, equipped with safety taps, similar to the one described above. Cooler outlet temperatures vary between 30° and 50°C, depending on environmental conditions (temperature, wind) and engine load.
Gas is introduced into the engine after being mixed with air in a gas carburettor.
Engine speed is controlled by-means of a Barber-Colman electronic engine speed regulator, which controls simultaneously a gas valve and an air valve. The engine speed is kept constant at 1500 rpm.
The system is equipped with an International Harvester gas engine (compression ratio 9.5 : 1), with a cylinder volume of 9.9 dm³.
The alternator is a short-circuit proof, self-excited internal pole machine in synchronous construction with the following specifications:
cos phi 0.8
The system is able to follow a step load change of 20 kVA with constancy of + 5 percent.
The alternator is equipped with a switchboard containing:
- 3 ampere meters
- 1 voltmeter
- 1 frequency meter
- fan control button
- ignition button
- start-up safety switch
- power socket CEE (5 pole) and power socket DIN 49462
A 24 V fan is provided for use during start-up of the installation.
Initially the product gas is flared. The flare is provided with a water lock in order to prevent backfiring.
During operation of the installation the fan batteries are continuously recharged.
Table 5.1 Performance Data for the Gasifier
The reactor and the filter box are provided with explosion discs.
Operating the start-up fan is not possible with valve E (see Fig. 5.1) opened, thus preventing air from being sucked into the system.
The engine is automatically stopped on loss of oil pressure.
The installation is provided with a suitable staircase and fuel feeding platform, in order to permit easy fuel delivery to the gasifier via the double-valve filling sluice. The whole installation is mounted on a base frame and can thus be transported without being dismantled.