Stochastic Modelling of Biomass Fuel Mix Cost for Boilers in Tea Processing

Abstract

Wood fuel is the main supply of heat energy for withering and drying of tea. With the diminishing trends of wood fuel caused by reducing land mass due to increased population and government ban on logging of wood fuel from the forest, tea factories are looking for alternative biomass fuels to supplement the wood fuel. However, most biomass are faced with uncertainties such as availability and calorific value which is affected by moisture content. This work presents a stochastic modelling approach for a reliable biomass fuel mix strategy of wood and macadamia nutshells taking into account the stochastic nature of the availability and calorific value of the biomass. These variables determine the quantity of biomass consumed to produce the required 400 kg of steam per hour at pressure of 10 bar and temperature of 180C. The variables also determine the cost of energy per kg of processed tea which affects the profits and competitive advantage of tea factories. The model generated randomly 40 values of moisture content between 12% and 50% and 40 values of wood availability between 60% and 100%. The moisture content and wood availability were used to calculate the energy content and mass of wood fuel used. The model subsequently calculated the mass of macadamia nutshells required to supply the deficit energy. In addition,the model calculated the total cost of the fuel mix. The model was iterated 20 times to generate more data sets to check the consistency of the model. Sensitivity analysis was also carried out to test the validity of the model. This model will be beneficial to the factory management and the Kenya Tea Development Agency in developing policy and strategies for biomass fuel acquisition. Keywords— biomass fuel , calorific value, fuel mix, moisture content, stochastic mode