Raising steam for your facility requires water, and depending on the steam plant’s size and design, the volume of feedwater needed can be small or quite large. Some applications allow for steam condensate to be recycled back to the boiler which is reused as part of the feedwater, with the rest coming in as fresh water, called makeup. The makeup water comes from your local utility or well water source. It is often cold and contains many dissolved gases, with oxygen being the most prevalent. Regardless of the volume of condensate returns you have, the makeup water needs to be conditioned before it can be used as boiler feedwater. The conditioning requirement for the boiler’s feedwater quality must achieve 4 goals, as outlined in both the 2015 ASHRAE Handbook chapter on Water Treatment , and the ASME Consensus on Operating Practices for the Sampling and Monitoring of Feedwater and Boiler Water Chemistry in Modern Industrial Boilers (CRTD-81). These goals are:
A deaerator is a specifically designed piece of equipment to achieve all 3 of these goals. Often the deaerator is a combination of two vessels; one vessel for removal of oxygen and non-condensable gases (scrubbing section), and a second vessel for storing hot feedwater (storage section). It is this 2 vessel design that provides superior results and efficiency as compared to simply having one steam heated “feedwater tank”. The deaerator’s scrubbing section mechanically breaks up the water into droplets so that oxygen and dissolved gases are removed from the water and vented out of the vessel before entering the storage section. The resulting high quality feed water has far lower concentrations of dissolved oxygen and non-condensable gases, as compared to a conventional feedwater tank, leading to minimized operating costs and improved steam quality.
As described above, the deaerator is far more effective than a steam heated feedwater tank because of its mechanical design and ability to use steam pressure and temperature to condition the makeup water into feedwater. The three main parameters indicative of a properly operating deaerator are temperature, pressure and dissolved oxygen removal. Ensuring these three parameters are within design limits is crucial for maximum performance and return on investment of the deaerator. The temperature and pressure should be checked at least daily, and logged in an electronic database for trending analysis. If fluctuations in temperature and/or pressure are observed, maintenance should be scheduled for the controls on the deaerator. Dissolved oxygen removal can be assessed by regularly scheduling a Dissolved Oxygen Study (DO2 study), which is a controlled test on the system that measures the dissolved oxygen level at the outlet of the deaerator. DO2 studies are important because they can identify when something has failed mechanically inside the deaerator, limiting its ability to remove oxygen or other non-condensable gases. A physical inspection of the deaerator will not often reveal if something has failed internally. DO2 studies should be scheduled at least on an annual basis, with the results logged and stored electronically for trend analysis. The DO2 study itself is relatively simple, but does require some planning and setup:
Your water treatment provider should be monitoring the temperature, pressure, and demand for chemical oxygen scavenger at least monthly, and logging this data into an electronic database for trend analysis. The easiest way to spot a failing deaerator is by observing changes in the “normal” levels of chemical consumed, or the relationship between pressure and temperature. Your water treatment provider should also be reviewing your daily logs of temperature, pressure and chemical consumption to spot potential issues. If you are doing your own DO2 studies, the water treatment provider should be using your data as well to help determine the effectiveness of the deaerator. At the very least, your water treatment provider should be performing a DO2 study themselves, to ensure the deaerator is functioning properly.
Your boiler mechanical contractor’s role is important as well, as they need to coordinate inspections and possibly repairs, in order to act on any deviations observed during the regular monitoring of deaerator performance indicators. A DO2 study will reveal incorrect deaerator operation, and often the fix is to repair/replace the spray head or a tray inside the “scrubbing” section of the deaerator. Bringing your mechanical contractor and water treatment provider together as a team is a great first step in ensuring your deaerator continues to operate at maximum efficiency.
WANT TO LEARN MORE?
Download our Engineering Note on Dissolved Oxygen Studies and Deaerator Efficiency.
Trade Expo / 05.14.19
Meet DuBois Technical Representatives at BOOTH# 5449, May 14-16 at EASTEC, to help shape your business at the East Coast’s premier manufacturing event. We will feature our leading our leading metalworking fluids, process cleaners, rust preventatives, paint pretreatment and water treatment solutions for cooling, boilers and wastewater.
Recent Events / 10.02.18
The acquisition of the Water Treatment Solutions division of Triwater Holdings LLC, and its Klenzoid, Eldon Water, Chemco Products and Nashville Chemical brands, expands DuBois position in Canada and enhances our solutions for the institutional, light industrial, food and beverage and natural resources markets.
Recent Events / 04.22.19
St. Joseph Mercy Oakland and Eldon Water, a recent acquisition of DuBois Chemicals, implemented a program to save a projected 665,000 gallons of water annually. For Earth Day this year, the hospital was awarded a $10,000 check by Eldon for being a sustainability leader.
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