Demonstration of a Condensing Economizer

Abstract

ABSTRACT Many industries and commercial operations depend on steam to provide thermal energy. Most small- to medium-sized installations are configured on low-pressure packaged boilers. These facilities cannot always use the same energy conservation measures (ECMs) as larger plants, and the application of an economizer is often overlooked. Economizers are frequently used to heat feedwater in large, high-pressure boiler plants and are an effective means to recover waste heat from flue gas. Considerable energy can be recovered, although it is normal to limit this practice to sensible cooling only. This prevents the formation of condensate and reduces the potential for any degradation of the boiler stack or economizer itself, though a significant amount of latent heat is lost. Economizers are not often used with small packaged boilers because the flue gas temperatures tend to be lower and the potential for heat recovery is limited. If designed appropriately, condensing economizers can alleviate these shortcomings and allow both sensible and latent heat to be recovered from the effluent gases. This article describes the assessment, installation and performance monitoring of a condensing economizer that was installed at a dairy in upstate New York with the assistance of the New York State Energy Research and Development Authority (NYSERDA). The low flue gas temperature (~350°F) from the boiler made the production of hot water for the plant's clean-in-place (CIP) systems more attractive than heating feedwater. Data obtained from the site showed that enough energy was recovered to offset 86 percent of the normal heating requirement and fuel consumption was reduced by more than 4,000 dekatherms. As a result, the flue gas temperature was reduced to an average of 140°F. The system required a minimum of maintenance and parasitic electricity to operate. Simple payback should be achieved in approximately four years.