An Experimental and Theoretical Study of Decentralized Gas Fired Liquid Heating

Sammanfattning: The effects on the energy situation in industry when gas fired liquid heaters replace steam have been determined by energy surveys performed in a brewery and a slaughterhouse, measurements of the performance and emissions from liquid heaters installed in these industries, and theoretical analyses of the potential energy saving. The theoretical study in the first part of the project provides information that allows assessment of the effects on the energy situation, of part or complete conversion to decentralized heating, under the conditions prevailing in the industries concerned. The second part of the project focused on increasing the liquid heater efficiency and reducing emissions of carbon monoxide and hydrocarbons. Heat transfer and pressure drop for a corrugated tube were investigated experimentally. Empirical correlations for heat transfer and pressure drop were developed. These correlations were used in the design model that was developed within this project. The design model was validated against experimental data and data from an industrial application, where a section of the smooth heat exchanger tube was replaced with a corrugated tube. The results show that the design model predicts the outlet flue gas temperature and the heater efficiency quite accurately. The wall temperature at the first corrugation is also predicted with reasonable accuracy. These results make it possible to calculate the location where a corrugated tube can be inserted without causing subcooled boiling or severe fouling. It is shown that emissions of carbon monoxide and hydrocarbons can be held at low levels, even when conventional industrial burners are used. The use of nozzles that produce long soft flames increases the risk for large emissions of hydrocarbons and carbon monoxide.