Electricity generation from palm oil biomass residues incineration : feasibility study with feedstock from governmental plantation sites in Sumatra Utara, Indonesia

Abstract

This thesis investigates the feasibility of communal electricity generation from feedstock originating from government owned plantation sites throughout Sumatra Utara. This region was selected due to the high concentration of palm oil plantations in the area, currently occupying of 15% of total land territory in the region. The city of Medan, an urban area with 2.1 Mio inhabitants, and capital of Sumatra, Utara, has relatively high grid connectivity and is therefore an ideal site for a palm oil biomass residue plant. The calculations done show that with the amount of feedstock from palm oil biomass residues of the government owned plantations in Sumatra, Utara, available it would be possible to power about five plants of 60 MW thermal power respectively of 21 MW generated electricity each. Thus, electricity of 105 MW, or during a year about 840 GWh might be produced. There are however limitations originating from the peculiarities of the fuel properties which impose difficulties for the operation of larger plants: - The humidity of the fuel mix of palm fiber and palm kernel shell is highly variable which requires a management of the humidity level by seasoning or torrefaction. - The palm oil biomass residues exhibit a relatively high nitrogen content, which may create high emissions of NOx. The operation of a staged fluidized bed combustor might reduce the NOx emission. If the NOx emissions still remain too high, then de-NOx systems involving ammonia injection will be necessary. - The palm oil biomass residues exhibit a relatively high ash content, with high concentrations of Na, K, Ca and Si. The resulting ash upon combustion exhibits a high alkalinity and a low melting point promoting bed agglomeration and liquid slagging, making the boiler more difficult to operate. For fuel with low melting ash fluidized bed combustion is likewise the recommended technique. - The high ash content requires increased efforts for limiting the emissions of fine particles. In order to meet fine particles emission standards for biomass power stations of the EU or US, in addition to cyclones either electrofilter or bag house filters will be required. - However, the alkalinity of the fly ash creates absorption sites for SO2, thereby reducing the emissions to a concentration below emissions standards. - The ash from a 60 MWth power plant operated with POBR is in the order of 700 kg/h (17 t/day), requiring silo transports back to the plantation, or to a suitable dump site, where the ash gets deposited and processed in a solidified form. Handling has to be taken with care due to the alkaline (caustic) properties of the ash. - Due to the many not completely resolved technical issues of POBR utilization for electricity generation a pilot plant of small size is recommended. - For a sustainable utilization of the POBR for power generation stack gas emission standards are to be defined.