Dealing with mercury from coal-fired power plants

Where does airborne mercury come from, and how do we get rid of it?

12/22/2011


Dear Control Engineering: When I read about new EPA regulations on mercury emissions from coal-fired power plants, I want to know where the mercury comes from, and how to get rid of it.

Power plants do not create mercury, lead, arsenic, or other heavy metals any more than they would be able to create gold. Those pollutants are elemental metals and present in coal. The problem is that when you burn coal, you vaporize those metals and send them out the stack. There is some controversy as to exactly what happens in the atmosphere, but eventually those metals condense, either in their elemental form or after reacting with something else in the process (e.g., chlorine), and fall to earth in rain drops. Rain goes into rivers and lakes, and fish accumulate the metals.

(There are other types of pollutants, such as dioxin, that can be formed in a combustion process, but that’s a different issue.)

Mercury emissions have gone down, at least as a function of total electricity produced, but many plants still have little in the way of abatement equipment. Conventional FGD scrubbers can help with mercury to some extent, but if you really want to cut it down, activated charcoal injection is usually best. If the fluegas is at the right temperature, mercury will condense and stick to finely-ground activated carbon particles blown into the stream. The particles are then removed in a baghouse.

This process works, but the result is contaminated charcoal. The usual disposal method is landfilling or burial. If you put it in an old coal mine, you’re returning it whence it came.

Peter Welander, pwelander@cfemedia.com



No comments
The Engineers' Choice Awards highlight some of the best new control, instrumentation and automation products as chosen by...
The System Integrator Giants program lists the top 100 system integrators among companies listed in CFE Media's Global System Integrator Database.
Each year, a panel of Control Engineering and Plant Engineering editors and industry expert judges select the System Integrator of the Year Award winners in three categories.
This eGuide illustrates solutions, applications and benefits of machine vision systems.
Learn how to increase device reliability in harsh environments and decrease unplanned system downtime.
This eGuide contains a series of articles and videos that considers theoretical and practical; immediate needs and a look into the future.
Controller programming; Safety networks; Enclosure design; Power quality; Safety integrity levels; Increasing process efficiency
Additive manufacturing benefits; HMI and sensor tips; System integrator advice; Innovations from the industry
Robotic safety, collaboration, standards; DCS migration tips; IT/OT convergence; 2017 Control Engineering Salary and Career Survey
Featured articles highlight technologies that enable the Industrial Internet of Things, IIoT-related products and strategies to get data more easily to the user.
This article collection contains several articles on how automation and controls are helping human-machine interface (HMI) hardware and software advance.
This digital report will explore several aspects of how IIoT will transform manufacturing in the coming years.

Find and connect with the most suitable service provider for your unique application. Start searching the Global System Integrator Database Now!

Infrastructure for natural gas expansion; Artificial lift methods; Disruptive technology and fugitive gas emissions
Mobility as the means to offshore innovation; Preventing another Deepwater Horizon; ROVs as subsea robots; SCADA and the radio spectrum
Future of oil and gas projects; Reservoir models; The importance of SCADA to oil and gas
Automation Engineer; Wood Group
System Integrator; Cross Integrated Systems Group
Jose S. Vasquez, Jr.
Fire & Life Safety Engineer; Technip USA Inc.
This course focuses on climate analysis, appropriateness of cooling system selection, and combining cooling systems.
This course will help identify and reveal electrical hazards and identify the solutions to implementing and maintaining a safe work environment.
This course explains how maintaining power and communication systems through emergency power-generation systems is critical.

(copy 5)

click me