No Boiler is an Island
Boilers make steam, but they don’t do it alone. Not for a long time, now. While early locomotive boilers consisted of a basic pressure vessel, heat source, pumps and all in one package, today’s stationary boilers have a range of sophisticated auxiliary equipment that can be added on to maximize every fuel dollar, minimize corrosion, and substantially prolong the life of a boiler.
A List of Villains
There are several factors that hinder boiler performance and longevity. Boiler tech has been fighting against them since the start, and we’ve made a lot of headway in the past few decades. Here are the worst offenders:
Corrosion
There are several ways that corrosion can form inside a boiler. Sediment, rust, magnesium, calcium, chlorides, the list goes on. When they come in contact with the heat of the boiler and the oxygen in the water, they start to chemically attack the metal surfaces in pipes, valves, and the pressure vessel.
Scale
Corrosion’s ugly cousin, scale, is also formed by dissolved solids in the boiler water. However, it doesn’t eat away so much as layer on. As impurities stick to the metal surfaces in your boiler, they start to collect and harden. When enough of them gather, they end up acting as an insulator, preventing heat from transferring efficiently between the heat and the water. That ends up requiring more fuel to produce the same amount of steam, and that’s just wasted money.
Oxygen
Boilers use water, and water is made up of oxygen (and hydrogen). So how can it be bad? When there’s too much oxygen dissolved in it. Dissolved oxygen is notoriously reactive, and will bond with all sorts of things. If it bonds with metal, it creates metal oxides which weaken and pits the structure of the metal. If it bonds with suspended compounds in the water or air, it can form harmful oxides that dissolve hard surfaces. To top it off, oxygen all by itself helps create electrochemical reactions between water and metal, causing the metal to break down.
Waste Heat
Ideally, you’d get the same amount of steam and heat out of your boiler that you put into it. However, this being the real world, it’s impossible to have every single BTU of heat energy work toward making steam. Right now, steam boiler efficiency tops out at around 85%, and that’s pretty impressive when you consider all the factors. Heat is lost by conduction through metal surfaces, and radiation through the air. Plus, since work processes aren’t 100% efficient either, there will always be leftover heat in the condensate once it stops being steam.
Imperfect Combustion
No matter how efficient your burners and how carefully you tune your combustion, you’re always going to have some heat left over in the exhaust gases. That heat is invariably lost when it goes out through the stack.
Low Water
If the water level in the pressure vessel drops too low, the walls of the pressure vessel can overheat and undergo substantial thermal stress. This not only shortens the life of the boiler, it can contribute to pressure vessel failure and leaks.
The Heroes of Our Story
As boiler technology has advanced, the industry has found newer and more innovative ways to tackle all the issues that hinder boiler life and performance. Most modern boilers will employ at least one of them, and some use all of them.
WATER TREATMENT
Proper water softening removes the harmful calcium and magnesium ions, replacing them with sodium ions in a process called “ion exchange”. As the water passes through a vessel packed with resin, the bad ions are stripped away and the less-harmful ions are substituted.
Modern boiler operation also uses a number of different chemical additives that reduce corrosion from oxygen, chlorides, and other suspended molecules, helping them all settle to the bottom of the pressure vessel where they can be removed with regular blowdowns.
DEAERATORS
Excess oxygen can be dissolved in condensate even if you can’t see it. The best way to remove it is by giving it an easy path out. Modern deaerators do this in one of two ways. Some deaerators use a method that involves spraying the condensate into fine droplets so the oxygen can float free as the water is heated. The other method involves cascading the condensate down a series of flat surfaces, allowing the condensate to spread out thin enough to rapidly heat and provide surface area so that the oxygen can escape.
ECONOMIZERS
Remember that waste heat we talked about? A stack/feedwater economizer is a last-chance heat exchanger on the stack to capture escaping energy. The heat that is in the surface blowdown? Blowdown recovery economizers do a great job of stripping that heat out of the condensate before it drains away. Employing a flash recovery section – otherwise escaping steam is routed to the deaerator to heat incoming boiler feedwater. Then the liquid remaining is passed through an exchanger where the heat is removed from the condensate, and passed to the feedwater coming from the softener. That’s like getting free BTUs added to your system. Preheating the feedwater with an economizer also helps to lessen thermal shock, and minimizes loss of steam production by the introduction of cold condensate.
CONDENSATE TANKS
If we dump water condensed in processes, a massive amount of cold water must be re-added to the system. Recovering, storing condensate, and pumping it back to the deaerator or boiler feed tank recovers that high quality H2O and puts it back to use.
BLOWDOWN SEPARATORS
If not handled properly, boiler blowdown steam can cause damage to the people and equipment around the boiler. Blowdown separators allow the blowdown to safely flash to steam in a controlled environment, and regulates the temperature of water going to drain.
BACKUP PUMPS
Every boiler has pumps to introduce feedwater, because the pressure vessel is under, well, pressure. Having a backup pump standing by can keep a boiler operating safely even if one of the main pumps fails.
FEEDWATER SYSTEMS
If a boiler runs out of water, that can necessitate the addition of untreated water just to keep it running. A properly sized feedwater system can keep the treated water flowing under any condition, preserving the life of your boiler and helping it keep running at rate.
GAS PRESSURE REGULATORS
By carefully controlling the amount of fuel coming into the boiler’s burner, combustion can be tuned to maximize energy efficiency. Gas pressure regulators in the gas train make sure the burner gets a consistent, steady, reliable supply of fuel at all times, so the boiler can run at its best.
CONTROL SYSTEMS
Boiler controls have come a long way. Today’s sophisticated controls, especially the AUTOFLAME systems, monitor everything going into and coming out of your boiler. They make hundreds of tiny adjustments every hour to keep fuel and air flowing at the right levels for optimal combustion, and monitor output to make sure the boiler stays efficient, and compliant with environmental regulations.
If you’re ready to trick out your boiler system with the latest and greatest equipment, one of WARE’s sales professionals can help you find out exactly how much energy you’ll save. If you’re considering a rental boiler, WARE has all of this equipment available as add-ons to any rental. And if you’re in the market for a new boiler system, we can build you the most efficient, capable boiler you’ve ever seen. Whatever you need, we’re here to help. Just let us know.