Practical Steps to Address Steam-Caused Industrial Power Plant Turbine Damage
By David C. Cline, Jr., Bryan Martin
This article discusses the selection, installation and initial operation of a turbine generator at a lumber mill designed to take advantage of excess steam capacity from boilers fired with a renewable energy source (primarily sawdust). A discussion of turbine damage after about one year of operation and subsequent mechanical, water treatment, and chemistry surveillance changes that were implemented are included.
The turbine discussed in this article is operated by Westervelt Lumber in Moundville, AL. Westervelt Lumber is a facility located approximately 17 miles south of Tuscaloosa, AL. It is one of the largest single site sawmills in the Southeastern United States and employs approximately 300 people. The sawmill processes 100% Southern Yellow Pine into various dimension, board, and timber products for use in industrial, commercial, and residential construction.
The mill operates two wood waste (green sawdust and bark) fired boilers, a Wellons boiler that started up in 1997, and a Teaford, which went into operation in late 2005. The Wellons boiler is an A-frame style boiler with four pile burning combustion cells that sit atop manually raked grates and is rated for 60,000 pounds per hour (lb/hr) steam production. The Teaford boiler, also an A-frame boiler is rated at 70,000 lb/hr capacity and has a Zurn-style sloped articulating grate. The steam from these boilers, a combined 120,000 lb/hr, is sent to the turbine at 600 pounds per square inch gauge (psig) and 725°F. Steam at 70 psig is extracted from the turbine and used in the mill's seven dry kilns as the heat source for the drying of lumber. The remainder of the steam is condensed in the condenser and returned to the deaerator for reuse.
Turbine Generator Project
The project that led to the installation of the turbine generator was in response to a request for proposals issued by the Alabama Power Co. (APCO). APCO is the local Public Service Commission regulated power provider for the Moundville, AL, area. APCO issued the request in order to add a renewable resource to their power production portfolio. At the time of the request, Westervelt Lumber's boilers operated at 125-psig saturated steam with an average production of approximately 90,000 lb/hr. The boilers were originally designed for 700-psig steam with the intent that if, at some future time, power rates increased to such a level that it would be a justifiable project. that the boilers would be rated appropriately. The APCO offering appeared to be such an event and an agreement was reached between APCO and Westervelt Renewable Energy (WRE) in mid-2010.
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