Heat transfer characteristics of a water heater operating on natural gas and cofiring with pulverized rumen contents

Abstract

This study discusses the heat exchange optimization of a 450 kW water heater operating with natural gas (NG) and in cofiring mode burning solid pulverized rumen and NG. The rumen material is a byproduct from cattle slaughter processes, consisting of the waste contained in the cow stomachs and intestines. In NG mode, the gaseous fuel provides 100% of the heat input, and in cofiring mode 50% of the heat rate input is obtained from the rumen contents and NG balances the heat rate. The paper presents experimental analysis on a scaled prototype of 45 kW, and the results are complemented with CFD analysis of the aerothermochemistry of the combustion chamber and heat exchanger. The heterogeneous reactions are stabilized using a low swirl injector. The optimization seeks to use swirling flows inside the combustion chamber to improve convective heat transfer from the combustion products to the water-cooled surfaces, and the use of decaying swirl generators to enhance heat transfer at the second and third gas passes. The geometry variations attain effectiveness above 86%, with low emissions CO, THC and NOx, and to attain reaction stability of the rumen biowastes.