Coal-Fired Power Plants Best Practices: Filtration and Lube

Submitted by Casey Sullivan
According to the United States Energy Information Administration, coal power accounted for 39 percent of the country’s electricity production last year.  Coal-fired power plants have been an integral part of the world’s power grid for the past century.  In a coal-fired power plant, coal is pulverized to a powder and strategically fed into a boiler along with preheated air where it is burned to generate heat.  Additionally, the boiler contains heat exchange tubes with water that is converted to steam in the plant’s boiler. The high pressure steam then acts as a catalyst to drive the turbines that ultimate drive a generator to create electricity.

The process sounds simple enough, but there are plenty of potential pitfalls and things to keep an eye on in order to avoid unnecessary shut-downs that can ultimately cost millions of dollars in lost energy.  It is difficult to go into too much depth about all the proper upkeep involved in keeping a coal-fired generation power plant online. However, for the purposes of this discussion, there are three main problems that often arise when running a coal-fired power plant. 

1) Turbine Reliability

Coal-fired power plants will often run continuously for several years between shut-downs.  Sometimes these shut-downs are planned for maintenance purposes, other times they are unexpected.  It’s the unexpected shut-downs that plant managers are always trying to avoid.  Unscheduled shut-downs are incredibly expensive, often causing millions of dollars in lost equipment, time and plant output.  This consequence directly speaks to how critical proper maintenance is on these plants. It is imperative the machinery be kept at a very high reliability level in order to avoid as many unnecessary shut-downs as possible.

More specifically, the turbines that drive the generator inherently have very tight tolerances between all of their moving parts.  The parts need to remain well lubricated so the tolerances do not break down.  Lack of lubrication will also cause equipment fatigue and more seriously, complete failure.  To ensure proper turbine reliability, lubrication is the key.  In terms of maintenance, unfortunately, lubrication is generally considered one of the lowest priorities — despite being arguably the most pivotal in terms of overall system functionality.  The subject of lubrication is an entirely separate topic, but often times there is a culture of complacency that exists toward lubrication.  Too often, plant managers will completely overlook lubrication requirements when mapping out the plant’s budget. 

2) Scaling from Poor Quality Make-up Water

The water used to feed the boiler can often lead to problems if not properly filtered and maintained.  Plants generally use what is known as make-up water in their systems.  This make-up water is typically provided from a natural body of water, usually a nearby river or lake.  Due to its nature, this make-up water contains both particulate and semi-solid biological material.  If not filtered correctly, these impurities will be precipitated out of the water directly on heat transfer surfaces.  This is known as scaling.  The evaporation in the boiler then causes the impurities to concentrate and can ultimately cause hot spots on the heat transfers.  Proper filtering of the make-up water is critical to eliminate scaling due to the high level of particulate. 

3) Plugging High Pressure Ash Wash Nozzles

During the course of the coal-fired plant’s operation, boilers will develop a significant amount of ash as they burn the fuel coal.  This ash will often affix to the boiler walls and to the internal heat exchange piping.  This makes it necessary to clean the boilers on a regular basis.  In order to do this, plants often use a high pressure water lance.  These water lances contain spray nozzles with extremely tight orifices.  These orifices, over time, can become plugged by contaminant from the water.  This goes back to making sure that the water doesn’t contain any particulate that would plug up the nozzles on these sprayers. 

4) Clean Boiler Fuel

The last pitfall to be aware of for this discussion is the contaminant that may be present in the boiler fuel.  The boiler fuel train contains a line to deliver fuel when the boiler is in startup.  All of this fuel will then remain on-line until the heat is at a temperature that is hot enough to sufficiently burn the fuel coal.  This start-up fuel needs to be properly filtered as well to remove any foreign contaminants.  If left unfiltered, the fuel has the capability to damage the heat transfer equipment in the boiler.

Proper filtration and lubrication are critical to the efficiency of a coal-fired power plant; however, they are only a few of the major elements that plant operators need to be aware of.

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