DESIGN, ANALYSIS AND FIELD TESTING OF LPG-FIRED FURNACES FOR BELL-METAL CRAFT
An integrated system of 'brass scrap melting' furnace and
'mould heating' furnace − both of 'natural-draft' type has been designed and tested in the field to be used by local handicraft artisans in the 'Bastar' region of Chhattisgarh, India. Selfaspirating LPG burners were used to fire the furnaces. Thermal energy of exhaust gases exiting the furnaces was partially recovered by pre-heating the scrap. Electrical power was required only to run a small centrifugal blower for 5 min to 10 min to increase the stack temperature rapidly so that draft can be created in the stack to start the process. After this, till the end of the process, the airflow required for combustion was able to sustain because of natural-draft created in the heated stack. The efficiency of the LPG-fired bell-metal furnace was measured as 3.7% as compared to 0.6% of the conventional wood-fired melting furnace. The LPG-fired mould-heating furnace had an efficiency of 16.4% in contrast with 1.9% of the traditional furnace. The total cost excluding labour was also nearly half of that of traditional firing, and the exposure to immense heat and smoke, which is a feature of the traditional firing process, was entirely done away with in the improved process with the new furnaces. The furnaces were very well received by artisans in the field.
For a suggested new design, where a single stack will be able to drive the gas flow through both the furnaces, steady sate mathematical modelling of the fluid flow and heat transfer in the entire unit was done to estimate the required chimney height. A code was developed in MATLAB® first without including radiation and subsequently including the effects of surface as well as gas radiation. Although the processes in the furnace are transient, in order to address the above issues, a steady state model was adequate. The pressure distribution obtained from the simulation qualitatively agrees well with the expected trends reported in the literature. The chimney height computed using the model is realistic, and the temperature distribution obtained by these simulations are indicative of the functioning of the furnace in the late stages of its operation.