Steam plays a key role at process plants — so a reliable cost-effective and safe boiler is essential. As facilities age, managers eventually must grapple with choosing between upgrading the current boiler or buying a new one.
Your existing boiler may be in good enough condition to justify repair or upgrade. However, that doesn't mean spending money on it makes sense. You must assess a variety of factors to see if modernizing your unit will suffice.
First, review in detail your current steam needs, regulatory requirements and fuel costs. In many cases, you'll find marked changes since that boiler was originally installed.
Plant steam profile. You must determine your current steam profile and loads. If load has significantly decreased, your boiler now may be running at a very inefficient low firing rate. Replacing it with a smaller unit or multiple smaller units might result in a substantial savings in fuel costs.
On the other hand, your plant load may have increased to the point where your boiler is being run at very high loads and is experiencing hefty maintenance costs. In this case, you might want to consider adding a new unit that can run more efficiently and keeping your current boiler as a backup.
Regulatory requirements. Local air regulations may have changed, reducing emissions allowed. Your existing boiler may not be grandfathered at its current levels, and so would require a retrofit. This might mean replacing the entire unit if the manufacturer doesn't offer just burner replacement. It might mean switching from oil to natural gas. Review of your local rules with a qualified environmental consultant will clarify what requirements you now must meet.
Fuel considerations. Fuel is by far the biggest expense in running a steam boiler. So, check the cost of fuel and the amount you use. Typically, efficiency improvement alone doesn't justify a complete boiler replacement. However, coupling that with spending otherwise necessary for a burner retrofit or boiler heat exchanger repair may.
The specifics of your existing equipment and your current and future needs will determine what can be done, what this entails and the cost.
In many cases a retrofit, that is, modernizing your current boiler, makes the most economic sense. Often it's easy to justify upgrading the control system with a state-of-the-art programmable logic controller and a new servo-based burner-management system. In addition, adding an economizer usually is a viable way to boost efficiency. However, repairing a boiler that's too small or inefficient may not be the best use of your capital budget. If you're looking to change your steam output or pressure, retrofitting generally isn't possible.
Even if your analysis indicates that you should get a new unit, consider whether it's worthwhile to do some minor repairs on the old boiler and keep it as a low-cost standby. And don't assume you should buy the same type of boiler.
TYPES OF BOILERS
Before choosing a new boiler, it's important to understand the types of units available. Almost all steam boilers are classified either as "fire tube" or "water tube."
A fire tube boiler typically is a horizontal vessel full of water with tubes running through it. The combustion gas flows through the tubes and heats the water around them. The gas can make from one to four passes through the water, depending upon boiler design. Another variation is the type of insulation, either dry back or wet back, on the end opposite the burner.
Typically, fire tube units run up to 1,000–1,500 BHP. Larger capacities require a water tube design.