F ut ure
BY DAN WALLACE
Dan Wallace is Vice President of Research & Development at
Preferred Utilities Manufacturing Corp.
Old boiler systems with outdated, inefficient equipment are the norm for
our industry. This is because boiler technology is largely stable, and boilers
are reliable pieces of equipment that can last decades. They are also expensive.
This means that boilers are only infrequently replaced, and boiler replacement
is often the only time that upgrading the rest of the system (burners, pumps,
control systems) comes up for discussion.
However, the world is rapidly changing. Electrical costs continue to climb,
petroleum and natural gas prices increase, and regulations on emissions
continue to tighten. Many outdated boiler systems are, or soon will be, prohibitively expensive to run and out of compliance with state and federal
We will examine components of the boiler system that can be replaced
without having to replace the boiler itself. In particular, we will present boiler
retrofits that can increase efficiency and prepare the system for the future.
Upgrade to Parallel Positioning or Fully Metered System
When we evaluate burner systems for upgrade potential, one of the first
things we look at is whether the system is using some sort of jackshaft linkage
or single point positioning. This antiquated technology is surprisingly com-
mon, and presents a relatively straightforward and inexpensive retrofit op-
portunity. But there are some things to look for and keep in mind.
Fuel and air must enter the burner at specific ratios and rates, and the ratios
vary with desired firing rates. This is because more excess air is required at
low firing rates than at high firing rates. So fuel and airflow (and potentially
other aspects of the system, such as recirculated flue gas) must be coupled in
a way that is sensitive to the firing rate.
Jackshaft linkages solve this problem in a straightforward mechanical way.
A single actuator controls the output of the system and is changed depending
on the firing. This actuator is attached to a jackshaft, which is in turn attached
to the fuel and air fan valves via linkage arms. Fuel and air flow ratios can