The thermoelectric plant proposed here is based on three process lines, which were developed so that the physic- chemical features of sludge meet the technical requirements of the plant: (i) three-phase continuous centrifugation; (ii) thermal drying; (iii) direct combustion followed by a vapor cycle, use of OMW as refrigerant in the condenser and con- centration with low temperature gases. The most relevant innovation introduced in this process lies in the fact that OMW is used as circulation fluid in the condenser, which leads to two main advantages: (i) part of the water con- tained in the OMW is evaporated inside the evaporation tower itself, using the residual energy of the cycle (at low temperature) – this leads to important savings in the energy needed in the drying place in order to obtain the biomass to feed the power cycle; (ii) the demand of water from area reservoirs is reduced.
Provided the scale economy is highly sensible in the case of small capacities, an economic analysis of the configura- tion for typical availabilities of sludge (120 · 103 t year 1) in olive-producer areas within a radius up to 35 km was carried out. The indicators used for such purpose were the net present value (NPV), the profitability index (PI), the internal return rate (IRR) and the payback time (PBT). This is followed by a sensitivity analysis in order to study the influence of possible oscillations in the vari- ables that may alter the NPV, regarded as the most rele- vant indicator.