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By Sheila Kennedy, contributing editor
Industrial and utility boiler systems alike are under increasing scrutiny for steam quality. Steam quality plays a significant role in boiler performance and efficiency, production reliability, and the longevity of the machinery itself. Steam system improvements can save 10% or more in fuel costs at a typical industrial facility, according to the U.S. Department of Energy (DOE).
“Each process needs a certain level of quality, pressure, and cleanliness of steam,” says Mike Pace, energy engineer for Horizon Energy Services (www.hs-e.com). “Steam is an effective way to transfer energy, but it requires a lot of knowledge to ensure that the system is installed correctly and running as efficiently as possible.”
Figure 1. The criticality of steam quality varies by application, but the best way to alleviate steam-quality issues is to maintain the quality of the water. (Source: Cleaver-Brooks)
Moisture in the steam can cause severe damage to the piping, valves, and other control devices, explains Nand Bogman, vice president of applications for Clayton Industries (www.claytonindustries.com). “The drier the steam, the more energy is contained in the steam delivered to the process,” says Bogman.
Although steam quality standards vary by application, common challenges are faced and the steps to achieving sufficient quality are shared:
The criticality of steam quality varies by application. “It depends on where the steam is used,” says M. Vasudevan, vice president of operations for Cleaver-Brooks (www.cleaverbrooks.com). “If it is used to drive a turbine, it’s a big concern because there’s an acceptable limit to how much silica/solids can be carried over. Once a turbine is coated with solids, it is less efficient and carries more weight. Similarly, in food applications, steam quality is a big issue. But for heating buildings, steam quality is less of a concern, and in oil sands, where steam is pumped in the ground to heat up and release oil, steam quality is not a concern at all.” (Figure 1)
Pharmaceutical companies need particularly clean steam, adds Pace. “They ensure quality through sampling and by making sure the boiler operates at the right temperature and pressure,” he says. “On the other hand, a school department can tolerate a 30-year-old boiler that has accumulated a lot of rust, but it can still increase its efficiency with the right technology.”
Figure 2. Inherent steam quality is based on conservative design of the boiler and the piping. (Source: Fulton Companies)
The greatest threats to industrial steam quality are maintenance and lack of knowledge of how the system is supposed to be running correctly, explains Horizon’s Pace. “A big problem is the graying of the industry, where older, experienced personnel are retiring and there is not a lot of young talent to fill their shoes,” he says.
“All too often, the new boiler designer does not have the decades of industrial steam experience required for a conservatively designed product that will deliver the required performance in a variety of challenging markets,” adds Melissa Wadkinson, chief engineer for Fulton (www.fulton.com) (Figure 2).
Not only is the workforce aging, but the assets are, as well. “The most pressing risk to boiler steam quality revolves around aging equipment, especially with regard to instrumentation and control,” says Ralph Porfilio, director of technology and application engineering for ABB's Power Generation business (www.abb.com). “So much of the equipment in industrial and utility power plants, not to mention the power grid in general, has outlived its life expectancy and is in need of either repair or replacement.”
Carryover, which results from incomplete separation of steam from the steam-water mixture in a boiler, is considered one of the greatest challenges in industrial boiler steam quality by D. Neil Bradwell, principal engineer for Indeck Keystone Energy (www.indeck-keystone.com). “Many factors, both mechanical and chemical, contribute to incomplete separation,” he says. “Mechanical factors include boiler design, inadequate or leaking separating equipment, high water levels, method of firing, and load characteristics. Chemical causes are high total solids concentrations, excessive alkalinity, and the presence of oily materials and other organic contaminants.” (Figure 3)