Dealing with combustible dust and controlling fuel spillage are struggles faced by almost all coal-fired power plants. During the ELECTRIC POWER Conference & Exhibition held Apr. 1–3, 2014, in New Orleans, La., several breakout sessions covered best practices being utilized at some facilities to overcome these challenges.
In one session, David Thomas, fuel systems manager for DTE Energy and chair of DTE Energy’s Combustible Dust Committee, explained some of the steps his company has taken to address housekeeping issues.
Thomas noted that auditing is an important part of his company’s plan. “Like any program, the key is accountability,” he said. During inspections, DTE reviews housekeeping plans and conducts walkdowns on fuel systems. Documenting and communicating observations is an important part of correcting any deficiencies found. Thomas said DTE’s process is based on a program developed by Luminant and observed during a benchmarking visit to Luminant’s Monticello plant.
An annual surprise assessment is also part of the DTE program. Risk management and insurance personnel get involved in that inspection, which takes place over a two- to three-day period and concludes with the generation of a comprehensive report. The intent is to obtain an honest evaluation and not just witness “window dressing” that can quickly be implemented prior to an announced visit.
Other actions that DTE has taken include installing carbon monoxide–monitoring systems with trending, which help identify smoldering hot spots, and using foam machines to help with cleaning. Thomas said the foam is sprayed on dirty walls to wash dust down to the floor, where it can be squeegeed down drains or collected and returned to the fuel supply.
Optimize Equipment for Your Situation
DTE has also utilized ASGCO conveyor belt wash boxes to help minimize dust and spillage at many of the company’s coal-fired plants. However, Thomas noted that it hasn’t had good experiences with all of the installations. “You can’t just assume that you can put in a piece of equipment and not have to maintain it and not have to maybe tweak it or mess around with it,” he said.
Joe Sander, power and mining manager for ASGCO, described for attendees how the wash boxes work. He explained that the conveyor belt enters the box and is hit initially with water from the first spray bar, which helps loosen any coal that is stuck to the belt. After that, it travels across a razorback secondary cleaner with tungsten carbide tips, which scrapes the water and coal off, so it falls into the pan. The spray box has a second spray bar and scraper just like the first that hits it again before the belt passes over a rubber squeegee that removes any remaining water prior to exiting the box. Sander noted that there is a hold-down roller on the top side that puts the proper amount of pressure on the belt to obtain adequate cleaning.
The wash box requires a water source, a drain, and labor to install. Sander recommended stainless or galvanized steel construction for coal plant use. DTE has found that a water regulator and control panel make the system much more reliable and trouble-free. Thomas said that DTE has also had to adjust nozzle sizes and install timed drain-flushing systems to improve operation.
Staff: The Key to Success
The biggest factor in the success of the wash boxes may be a culture shift among operators. Once the bugs were ironed out and the system was working as designed, operators could see the benefits. Based on air quality dust tests at DTE’s River Rouge plant, the wash box improved air quality by over 60%. Now, when defects arise, the items are turned into emergent work requests, and operators who were initially against the system, insist that it be kept in operation.
—Aaron Larson, associate editor (@AaronL_Power, @POWERmagazine)