|Low Cost Charcoal Gasifiers for Rural Energy Supply (GTZ, 1994, 49 p.)|
|7. Derived technical demands for field application of gasifier-engine systems|
It is a decisive advantage of the ferrocement gasifier that no corrosion of materials is to be expected. Whereas all metal plants-if not made of expensive stainless steel-corrode rapidly and have to be repaired by welding or replacement of components after one or two years, the ferrocement vessels and tubes are basically maintenance-free. This is especially important when the gasifier is not used all year round. A metal gasifier will just corrode away if it is left for some month without having been carefully cleaned and painted. A ferrocement gasifier is not affected at all by moisture and climate.
If there appears any rupture during operation, this may be the result of overheating when not enough cooling water was used. In that case, however, the repair is very easy by just chiselling up the rupture and adding new mortar to it.
A repair which is frequently necessary at classical metal gasifiers is the replacement of sealing ropes, nozzles, threaded tubes, hinges and so on - all these parts are affected by heat or corrosion. These sensitive parts are virtually non-existent at the ferrocement gasifier. The simplicity of the design avoids nearly all of the traditional repair problems.
The only necessary maintenance work is the replacement of the filter bags, when they are too contaminated. It is recommendable to have a second set at hand. The replacement is then done in 10 minutes. The replacement intervalls depend on the average load of the system; as a rule of thumb, every 100 hours (or once a month) is a typical interval. Diagr. 5 shows the average pressure drop across the filter section at various loads.
Diagramm 6 shows the pressure drop across the filter system over a period of 3.5 hours and over two subsequent test runs. It can be seen that a self-cleaning effect takes place: By the sudden collaps of the filter bags, when the suction of the engine stops at the end of a run, the dust layer on the filter clothes is partly removed.
A pressure gauge at the gas outlet is a very recommendable device for control of the filter performance. Even if the operator is experienced enough to know when the filter has to be changed normally, a defect in a filter bag can result in a clogging of the safety filter and a decrease of engine power.
Events of that kind are indicated by a sudden increase of the pressure drop across the filter units.
The ash removal from the ash container (under the reaction cylinder) should be done daily, together with the cleaning of the grate, before the new start. It is recommendable to let a layer of ash or sand continuously at the bottom of the ash box as a thermal protection of the cement.
The removal of deposits in the two settling chambers should be done once a month (together with the servicing of the filter bags).