Water treatment: Getting it right in the boilerhouse

One of the most important principles of good water treatment is to provide the boiler with the best quality feedwater that we economically deliver.

07/11/2013


Courtesy: Spirax SarcoWater softener: Why use it?

One of the most important principles of good water treatment is to provide the boiler with the best quality feedwater that we economically deliver. Feedwater is made up from a mixture of site supply (make–up) water and pure condensate. The level of impurities in the make-up water is the key deciding factor in minimizing deposit build-ups in the boiler. The most common impurities are calcium and magnesium which when present are collectively known as “hard water.” Left to accumulate to uncontrolled levels in a boiler, these “hardness” contaminates will form thermally insulating boiler scale deposits at boiler hotspots such as boiler tubes. This results in rapidly increased fuel usage and boiler operating costs as the boiler struggles to burn more fuel under reduced efficiency to meet steam demand. The resulting increase in fuel costs often exceed the cost of maintaining a chemical treatment program by a factor of ten or more over a 12 month period.

Water softeners remove hardness from the feedwater to produce “soft water” and thereby minimize the risk of scale in boilers.”

Selecting a softener?

The most commonly used softener is the zeolite type that consists of a softener exchange vessel, control valves and piping, and a system for bringing, or generating, the resin.

The softener tank is usually a vertical pressure vessel with an inlet distribution system, free-board space, a regenerant distribution system, ion exchange resin, and a resin-retaining underdrain collection system. Selecting the correct softener for your boiler feedwater involves considering the following:

  • Sizing to handle peak water flow demand
  • Testing make-up water to ensure adequate softening capacity
  • Adequate regeneration options to reflect plant operating loads

While easy to maintain, and replenish with salt, softeners require regular monitoring to ensure peak performance and maximum resin life. In areas where make-up water is hard, temporary softener failure can lead to rapid scale formation on boiler tubes, so proper softener selection and monitoring is essential.

pH control of boiler water

Mild steel is an “amphoteric” material meaning it will be reactive with both acid and highly alkaline water. To minimize corrosion, boiler pH is controlled in a range between pH 9.0 - pH 12.5 depending on the make-up water characteristic, boiler pressure and metallurgy. A localized area of either low or high pH in a boiler is the second most common cause of boiler corrosion behind oxygen corrosion.

At boiler temperatures and ideal pH conditions, mild steel passivation results in the formation of magnetite, a black iron oxide film that acts as a barrier between boiler water and steel. The corrosion reaction stops after a uniform magnetite layer is formed.

Rapid general corrosion can happen if this protective film is disrupted, so water chemistry must be carefully controlled to maintain the film. An acidic condition can destroy the magnetite film, while a highly alkaline condition can cause caustic gouging. A “pH excursion” will often show itself as black boiler water in the sight glasses as the magnetite layer is lifted off the tubes.

Control of pH is important for the following reasons:

  1. Corrosion rates of metals used in boiler systems are sensitive to variations in pH
  2. Low pH or insufficient alkalinity can result in corrosive acidic attack
  3. High pH or excess alkalinity can result in caustic gouging/cracking and foaming with resultant carryover
  4. Good pH control is essential to form the protective magnetite film

Content provided by Spirax Sarco, originally published in Steam News Magazine.



No comments
The Top Plant program honors outstanding manufacturing facilities in North America. View the 2015 Top Plant.
The Product of the Year program recognizes products newly released in the manufacturing industries.
Each year, a panel of Control Engineering and Plant Engineering editors and industry expert judges select the System Integrator of the Year Award winners in three categories.
2017 Lubrication Guide; Software tools; Microgrids and energy strategies; Use robots effectively
Prescriptive maintenance; Hannover Messe 2017 recap; Reduce welding errors
Safety standards and electrical test instruments; Product of the Year winners; Easy and safe electrical design
Infrastructure for natural gas expansion; Artificial lift methods; Disruptive technology and fugitive gas emissions
Mobility as the means to offshore innovation; Preventing another Deepwater Horizon; ROVs as subsea robots; SCADA and the radio spectrum
Future of oil and gas projects; Reservoir models; The importance of SCADA to oil and gas
Diagnostic functions for system safety; Specifying industrial enclosures; Effective decision support for a crisis
Transformers; Electrical system design; Selecting and sizing transformers; Grounded and ungrounded system design, Paralleling generator systems
Natural gas for tomorrow's fleets; Colleges and universities moving to CHP; Power and steam and frozen foods

Annual Salary Survey

Before the calendar turned, 2016 already had the makings of a pivotal year for manufacturing, and for the world.

There were the big events for the year, including the United States as Partner Country at Hannover Messe in April and the 2016 International Manufacturing Technology Show in Chicago in September. There's also the matter of the U.S. presidential elections in November, which promise to shape policy in manufacturing for years to come.

But the year started with global economic turmoil, as a slowdown in Chinese manufacturing triggered a worldwide stock hiccup that sent values plummeting. The continued plunge in world oil prices has resulted in a slowdown in exploration and, by extension, the manufacture of exploration equipment.

Read more: 2015 Salary Survey

Maintenance and reliability tips and best practices from the maintenance and reliability coaches at Allied Reliability Group.
The One Voice for Manufacturing blog reports on federal public policy issues impacting the manufacturing sector. One Voice is a joint effort by the National Tooling and Machining...
The Society for Maintenance and Reliability Professionals an organization devoted...
Join this ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis...
IMS Research, recently acquired by IHS Inc., is a leading independent supplier of market research and consultancy to the global electronics industry.
Maintenance is not optional in manufacturing. It’s a profit center, driving productivity and uptime while reducing overall repair costs.
The Lachance on CMMS blog is about current maintenance topics. Blogger Paul Lachance is president and chief technology officer for Smartware Group.
The maintenance journey has been a long, slow trek for most manufacturers and has gone from preventive maintenance to predictive maintenance.
Featured articles highlight technologies that enable the Industrial Internet of Things, IIoT-related products and strategies to get data more easily to the user.
This digital report will explore several aspects of how IIoT will transform manufacturing in the coming years.
Maintenance Manager; California Oils Corp.
Associate, Electrical Engineering; Wood Harbinger
Control Systems Engineer; Robert Bosch Corp.
This course focuses on climate analysis, appropriateness of cooling system selection, and combining cooling systems.
This course will help identify and reveal electrical hazards and identify the solutions to implementing and maintaining a safe work environment.
This course explains how maintaining power and communication systems through emergency power-generation systems is critical.
click me