Eastman Chemical Company: Power Department Staff Engineer Helps Find New Energy Efficiency Opportunities for Boilers
Eastman found new opportunities for energy savings by focusing on two existing coal-fired stoker boilers at its Kingsport, Tennessee, facility. The Power Department staff engineer spearheaded the effort to evaluate the efficiency of two existing boilers and to determine what, if any, opportunities there were for performance improvements. The commitment and leadership required for this boiler improvement project was recognized through the Department of Energy’s Individuals Taking Energy Action in Manufacturing (ITEAM) Prize.
The staff engineer’s first step was to evaluate the baseline boiler efficiency using two years of historical station instrument data. Following the American Society of Mechanical Engineers (ASME) Performance Test Code (PTC) 4, the data was compared to the predicted performance parameters provided by the original equipment manufacturer. The PTC 4 process helps to define the method, calculations, and test requirements for determining the efficiency of fired steam generators. The study revealed that both boilers were suffering from excessive dry gas losses due to air-in leakage and high excess air levels.
The modifications allowed the boiler to be operated at a much lower excess air level than thought possible and improved the control loop response times. This improves response to load swings and reduces dry gas losses. The combination of new stoker doors, improved door seals, and the elimination of a slip joint reduced tramp air leakage into the boiler, which coupled with the control improvements, led to an overall reduction of gases moving through the boiler. This resulted in lower power requirements for both forced and induced combustion draft fans, and the boiler now runs at a lower excess air level without overheating, which improves combustion and reduces heat in the front of the boiler.
To quantify the effectiveness of the boiler improvements, the Eastman team followed the ASME Performance Test Code 4 to calculate efficiencies and coal consumption. Electricity consumption and steam consumption of auxiliary fans were measured using station instruments or calculated using fan curves and basic thermodynamics. The energy consumption was then measured at several load points thirty days after the project implementation date. The load point time stamps were a minimum of one hour and up to several days long. The results were averaged into steam load groups from 190-200 thousand pounds per hour (KPPH), 220 KPPH, and 240 KPPH. Performance data was then compared from pre-project to post-project at each load point to estimate the impact of the improvements.
The upgrades have resulted in a sustained decrease in energy consumption of Boilers 23 and 24 which has yielded cost savings of $2,100,000/year in fuel and utilities costs. The savings are based on before and after annual comparisons of PI data and ASME PTC based boiler efficiency calculations. The efficiency of boilers 23 and 24 increased by an average of 4.43%, lowering fuel consumption. The success of the project led the staff engineer to create an Equipment Performance Team within the Power Department where staff now have a forum to share learnings and support other projects targeting additional boilers in the fleet.