If you’re new
to the field of
boiler control systems
or a veteran wanting
new insights, these
boiler control resources
will help guide
you in the right
direction.
Jerry Gilman
This book addresses issues to be considered when defining measurement transmitters and specification for transmitters. Final control elements are reviewed as to characteristics and sizing. Engineering details on control systems and the setup of the various control functions are covered with specific examples of boiler control including configuration and tuning.
Preheat combustion air and absorb additional heat from flue gas.
Format: Softbound Book – 2005 ISBN: 978-1-55617-907-5 Length: 144 pages; Weight: 1 lb. Member: $59.00; List: $69.00 www.isa.org/boilereng
The Control of Boilers, 2nd Edition S.G. Dukelow This classic resource helps you reduce boiler operating costs through a detailed explanation of all aspects of boiler processes. It presents the basics of boiler control, the interrelationships of the process characteristics, and the dynamics involved, with emphasis on start-up, shut-down, flame monitoring, and safety interlock measures.
Format: Hardbound Book – 1991 ISBN: 978-1-55617-330-1 Length: 412 pages; Weight: 3 lbs. Member: $69.00; List: $79.00 www.isa.org/boilercontrol
Where there’s steam there’s water, and where there’s water there’s probably corrosion. In the power industry, it is a persistent phenomenon that is difficult to control. In the paper industry, harsh chemicals are the corrosion culprit. Preventing corrosion doesn’t call for a one-size-fits-all solution. Suppliers, integrators, and users agree, corrosion prevention means billions of dollars a year, and they offer strategies and techniques for their varying corrosion conundrums.
“If we didn’t have reliable instrumentation to tell whether we were at the low levels, we’d take the conservative approach and treat to eliminate the oxygen, which means we’d spend the $100k a year” to avoid destryoing the boiler pressure system.
Along with corrosion come deposition, scaling, and deposits that fall out of water and collect on condensers and heat exchangers. Corrosion can occur more rapidly as these impurities concentrate in under-deposit corrosion (deposits that stick to the metal surfaces inside these systems). “We always talk about corrosion and deposition together, and in water chemistry, it’s difficult to control,” said Brian LaBelle, power industry manager at Emerson Process Management in Irvine, Calif. In a power plant, it can change fast because large quantities make up steam losses.
These power plants boil tons of water to turn turbines to contain steam. As the steam goes away, they need to replenish with makeup water. Ground and city water have elements that, left untreated, will cause corrosion. Chemicals such as ammonia added to water to raise pH levels can create a slight alkaline environment to add protective coating on metallic surfaces that come in contact with water.
The power industry is responding to this by monitoring dissolved oxygen, LaBelle said. Companies use sensors sensitive to parts per billion (ppb) levels of oxygen to help control the pH, but adding ammonia to raise pH can create another corrosion problem. Using deaerators to get rid of oxygen raises water temperatures, which introduces oxygen scavengers such as hydrazine.
Some avant-garde ways to measure dissolved oxygen are sensitive and less expensive sensors with self-depleting designs, also called membrane-based amperometric sensors. The self-depleting design means there is oxygen inside the sensor that it has to consume. “When you put these things together for the first time before you put them into service, there’s atmospheric oxygen to consume,” LaBelle said. Some of the more recent innovations are the sensors that deplete themselves rapidly of internal oxygen. “Every time you take the sensor out to clean or calibrate, you expose it to atmospheric oxygen, more than what you use in a power plant. The faster it can consume oxygen in air during maintenance, the better the sensor,” he said.
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