The citrus industry is of great importance in Tucuman, being in the top spots worldwide. Peel drying during lemon processing, has the highest consumption of natural gas, which comes into deficit at harvest time. Large amounts of biomass waste are generated from lemon cultivation, which can be exploited by gasification: a thermochemical conversion process of a solid or liquid fuel into a gas by incomplete combustion. The aim of this study was to evaluate technically and economically a gasification plant of biomass residues from lemon harvest to supply energy to the lemon peel drying of a factory processing 50 t/h located in Lules (Tucumán, Argentina).

Availability and energy potential of residual biomass were analyzed. Process was defined including: transport of biomass wastes to the gathering centers; preconditioning; transportation to the factory; drying of the chips; gasification and lean gas cleaning; poor gas combustion; mass and energy transfer in peel drying. The equipment required for the processing and transport of biomass were identified and quantified. A system of equations from mass and energy balances and sizing of the wood chip dryer was raised. For economic and financial analysis of the project, investment, operating costs (ranked as fixed and variable costs) were identified and quantified, and then the cash flow was calculated. From cash flows, the equivalent annual costs (EAC) of the project and the current situation of the factory were calculated for comparison. The project was analyzed in three scenarios: without bank credit, with bank credit, and selling carbon credits. The sensitivity of EAC of the project and the current situation was performed regarding the most important variables.

As result, the study determined the need to install two collection centers of 1.3 ha received 8.639 t / month of biomass with 50 % humidity, located at a distance of 5 km from the factory to the north and the south, respectively. The gasification plant attached to the factory process 3,960 kg / h of chips at 15% moisture, producing 12.657 kW of thermal energy with 9.900 Nm3 / h of poor gas. Sizing of the rotary dryer chip, energy integrated with peel driers, with moisture gradient of 30 % to 15%, results in a diameter of 3 m and a length of 11.8 m. The initial investment for the project is 49 million pesos, with total annual costs of about 6.5 million. The distance from the collection centers and fuel costs showed not to have significant impact on EAC. The EAC of the current situation is equal to the project with bank credit rate of 19% annual interest and selling carbon credits at 6 € / tCO2.