Condensing economizers for small coal-fired equipment

摘要

Condensing economizers can be used to increase the thermal efficiency of boilers and furnaces. This study focuses on evaluating indirect contact economizers as applied to heating equipment burning coal-water mixtures although the results can be extended to other fuels. In addition to dry gas sensible heat, latent heat is recovered from flue gas water vapor, improving system efficiency markedly. In addition to improving thermal efficiency, condensing economizers can also capture particulates. In tests to date up to 98% total removal has been measured. The primary objectives of this project are to evaluate the most important mechanisms involved in particle capture and to enhance capture in practical systems. The intent of the work is to contribute to the ongoing program at the Department of Energy/Pittsburgh Energy Technology Center in the development of coal-fired combustion equipment. These results are expected to be most applicable to smaller scale equipment where the low temperature heat from the economizer can be used. However, interest in the use of condensing economizers for industrial and utility applications is increasing and this work certainly is relevant in these sections also. The approach involves determining thermal efficiency improvement and particulate removal efficiency (experimental), and developing models capable of predicting system performance under varied operating conditions (theoretical). Gas temperature and condensation profiles through the economizers have been predicted and overall predicted performance are consistent with test results. Mechanisms for particle removal are discussed in this paper and predicted removal efficiencies as a function of particle diameter are presented.