Steam Conservation and Boiler Plant Efficiency Advancements

Abstract

This paper examines several cost-effective steam conservation and boiler plant efficiency advancements that were implemented during a recently completed central steam boiler plant replacement project at a very large semiconductor manufacturing complex. The measures include: 1) Reheating of dehumidified cleanroom make-up air with heat extracted during precooling. 2) Preheating of deionization feedwater with refrigerant heat of condensation. 3) Preheating of boiler combustion air with heat extracted from boiler flue gas. 4) Preheating of boiler feedwater with heat extracted from gas turbine exhaust. 5) Variable speed operation of boiler feedwater pumps and forced-draft fans. 6) Preheating of boiler make-up water with heat extracted from boiler surface blow-down. The first two advancements (steam conservation measures) reduced the amount of steam produced by about 25% and saved about $1,010,000/yr by using recovered waste heat rather than steam-derived heat at selected heating loads. The last four advancements (boiler plant efficiency measures) reduced the unit cost of steam produced by about 13% and saved about $293,500/yr by reducing natural gas and electricity usage at the steam boiler plant. The combined result was a 35% reduction in annual steam costs (fuel and power).