Sustainability Assessment of Co-firing of Coal with Wooden Biomass in 110 MW TPP Kakanj Unit 5

摘要

In this paper, sustainability of co-firing schemes in Thermal Power Plant Kakanj - the power station within Bosnian power company JP Elektroprivreda BiH d.d. Sarajevo - is under consideration. The Project is aimed to meet rising CO_2 reduction requirements that the mentioned power company is supposed to fulfil on the base of the agreement with Bosnia and Herzegovina Government following the EU Joining Map. The plant under consideration is 110 MW TPP Kakanj Unit 5 - coal-based power plant fully reconstructed in 2004 with installed low NO_x burners and OFA system. The PF boiler type with slag tap furnace is fuelled with the brown coal from nearby coalmines of Middle Bosnia. Technological, economical, environmental and social aspects of the different options of the unit operation are considered within the analysis. The experimental lab-scale facility PF entrained flow reactor was employed to optimize the coal-biomass blends, in order to reduce impact of co-firing regimes on the boiler efficiency. The experiments have shown that 7%-share of wooden biomass -spruce sawdust can be fired with the brown coal used in TPP Kakanj Unit 5 without serious impact on continuous slag flow and without major problems on slagging and fouling. Economical analysis is related to evaluation of costs of collecting, transport and storage of wooden biomass on sites, costs of the preparation of the wooden biomass into suitable form for PF combustion, as well as necessary adoption of the feed and firing system of the boiler. This analysis has resulted in determination of economic indicators, namely: indicator of investment, indicator of fuel costs and indicator of O&M costs.Several options of biomass feed were considered, among the option of blending the chipped wooden biomass with coal on the coal depot is ranked as a preferable option. Respecting environmental issue, emissions of NO_x and SO_2 for the co-firing regimes are prospected on the base of the results from the experimental lab-scale furnace. Thus, 7%w of the biomass replacing the brown coal used in TPP Kakanj unit 5 results in 15% of SO_2 reduction thank to less sulphur in the fuel and more convenient Ca/S molar ratio. In the same time, no clear relation between biomass share and NO_x emission could be recognized by the experiments performed, and overall NO_x reduction is till 5%. Furthermore, emission of CO_2 is calculated by EMEP-CORINAIR methodology for different options of co-firing schemes; for the case of 7% of biomass, annual CO_2 reduction is 64838 tones - calculated for an average time availability of the Unit of 83%.The assessment has shown good opportunities of the co-firing regimes for case of TPP Kakanj, particularly in the line of reducing fuel costs and reductions of SO_2 and CO_2. The assessment should help the decision makers to move the action.