Improvement of Furnace Efficiencies: Evaluation from Operational Data and Case Histories

Abstract

This paper presents methods which can be used to determine heater and boiler performance from operating data. A study is presented delineating the variation of combustion efficiency with load, excess air, and stack and wall losses. The results indicate that over an operating range of 25-100% of maximum load, combustion efficiency values lie within a band of 1.5%. A preliminary efficiency function can be obtained from one operating point and two calculated points. As excess air is increased the inside wall temperature and wall loss decrease, but the stack temperature increases and the efficiency decreases.

The methodology is applied to eight operating cases, ranging from 50 to 100 million BTU/hr; and include gas, oil, and coal fired units, currently in service in petrochemical plants, refineries and an electric utility plant. The individual analyses lead to the following conclusions: The figure of 92% as a practical upper limit to efficiency is strongly confirmed; substantial improvements in combustion efficiency is strongly confirmed; substantial improvements in combustion efficiency can be attained, up to the range of 87% to 92%; where earlier retrofit has already been accomplished, 87% may be the economic upper limit.