Investigations into the utilisation of chicken litter for power generation

Abstract

Chicken litter is commonly used as bio fertilizer or soil ameliorant due to its high content of nutritional components such as nitrogen (N), phosphorus (P) and potassium (K). Oversupply of chicken litter to land, however, may cause problems due to the built-up of excessive nitrogen which oxidises, forming nitrates and ammonia compounds. The highly concentrated nitrates can contaminate both surface water and groundwater, which are sources of drinking water. Evaporation of ammonia also causes odour problems in the surrounding areas. With fast increasing chicken production, and limits on the use of chicken litter as fertilizer on local farms an alternative utilisation approach is the use of chicken litter for energy production. Energy production from chicken litter is of particular interest in developing countries where electricity supply from the grid may not be existent or is highly unreliable. Possible technologies for the conversion of chicken litter to energy are combustion, anaerobic digestion, gasification and pyrolysis. Literature review of these methods has indicated that considering energy conversion efficiency, economic and environmental factors, pyrolysis can be a suitable method for application in developing countries such as Indonesia. For this reason, this thesis focuses on pyrolysis and its potential to produce char, syngas and bio oil yield. Three types of pyrolysis have been studied. These include: slow pyrolysis in the temperature range 350°C - 450°C, intermediate pyrolysis at the temperature range 500°C -700°C and fast pyrolysis in the temperature range 400oC – 600oC. The types of chicken litter used as the feedstock in slow pyrolysis were hay mix (chicken manure + hay), straw mix (chicken manure + straw), rice husk mix (chicken manure + rice husk), wood shavings mix (chicken manure + wood shavings). For the intermediate pyrolysis, fresh chicken litter (FCL) from Ireland and pelletized chicken litter (PCL) from Finland were used. For the fast pyrolysis experiments, only PCL was used. The result of the chicken litter pyrolysis experiments showed that the dominant product was char in the slow pyrolysis, liquid (bio-oil) in the intermediate pyrolysis and gas (syngas) in the fast pyrolysis. In addition to the experiments, simulations were performed using Aspen plus, to determine the maximum amount of electric energy that can be generated from the pyrolysis of chicken litter. The simulations were based on chicken litter from a farm with a production of 400,000 birds/batch. Liquid yield was determined from the experiments to have the highest calorific value, and thus, the simulations were performed using the parameters and results from the experiment that generated the highest level of liquid yield-this was the FCL pyrolysis at temperature of 500 °C. The simulation revealed that the heat from the combustion (burning) of all gas yield plus 35% of char yield would be sufficient to serve as the heat input for pyrolysis process. The heat from combustion of the liquid yield was then used as the energy input to an ORC system to generate electrical power. The results showed that the system with could produce electrical output of around 150 kW with an overall conversion efficiency of 6.5%. Economic analysis using the Net Present Value (NPV) methodology and investment conditions in Indonesia has shown that, assuming all the electrical energy generated and 65% of the char yield is sold, the system would produce a return on investment of 9 years. Improvements in ORC efficiency and reduction of capital cost as well as reduction in interest rates (currently 12% in Indonesia) is expected to lead to increased return on investment and improved viability of these systems for both energy security and reduction of environmental impacts in developing countries.