Boiling it all down

When building, designing, and specifying boilers and boiler systems, consider not just the monetary lifecycle, but also the environmental lifecycle of the design.

04/01/2008


When building, designing, and specifying boilers and boiler systems, consider not just the monetary lifecycle, but also the environmental lifecycle of the design.

Systems should be designed from cradle to grave, or better yet “cradle to cradle.” To summarize some of the concepts in “Cradle to Cradle: Remaking the Way We Make Things” by William McDonough and Michael Braungart

Premature failures mean reduced life and emergency replacements. Engineers must design to prevent premature failures.

Many times, proven boiler system designs can and do stay in service for 30 years or more—if properly designed, operated, and maintained. In boilers, most premature failures come from thermal shock, poor water quality, and misapplication.

System designs that hit a hot boiler with a slug of cold water or system designs that don’t maintain a minimum flow through the boiler can cause thermal shock. For applications that require these specific designs, specify boilers designed for reduced susceptibility to thermal shock. Poor water quality in hot water boilers generally is caused by either failure toproperly initially treat water, or by leaks that go unrepaired and result in loss of treatment and introduction of corrosive raw water into the system.

Poor water quality in steam boilers comes from a myriad of reasons: failure of treatment systems, failure of manual or automatic blowdown, or excessive make-up. For a boiler system that supplies mostly humidification (a high make-up system), consider point-of-use steam to steam humidifiers, or an unfired steam generator with materials of construction (including pipe valves and fittings) that are designed for the untreated boiler water that is the norm for humidification steam today. This substantially closes the loop on the fired boiler system, greatly increasing its life. Don’t forget the automatic blowdown system for unsupervised steam boilers and steam generators.

Selecting for efficiency

Higher efficiency means lower operating cost, possible higher first cost and also reduced life. The case in point here is condensing gas boilers. The acidic condensate from the products of combustion will react with the metal in the condensing portions of the heat exchanger and the drainage path and may cause them to fail before the rest of the unit. In evaluating a condensing boiler design, ask the manufacturer what parts can be replaced and the cost of the parts. Compare materials of construction and corrosion allowances. Ask manufacturers what spare parts they recommend and specify sets to be included with the boilers. Ask manufacturers about their equipment’s typical service lives of their and find out their warranty policies and lengths. Ask to see boilers of theirs that is five or more years old and applied in condensing applications.

For a new space-heating system with a condensing boiler, remember to maximize the time the system can operate in its condensing mode. Look at designing the system to produce peak output at 140 F or lower water supply temperature. If you have spent your career designing at 180 F water supply temperature and 20 F %%TRANGL%% T, you will find yourself looking at radiant floor systems, more rows in the coils, and more surface area in the radiators.

Don’t give up hope for a renovation of an old system that was designed for 180 F or higher water temperatures. Commissioning agents have found that there are quite a few systems out there that are so conservatively designed at 180 or 200 F that operate well at much lower temperatures.

Bells and whistles

In specifying coil tube thickness for hydronic coils, particularly for air handlers, consider a wall thickness greater than the minimum thickness offered to get the pressure rating to extend the life of the coils. This allows for some internal corrosion that can result from poor water quality, and will allow for some metal loss from coil cleaners and external corrosion.

Ask your boiler vendor what options they offer in the areas of controls and trim that can extend the life of the system and improve operating efficiency (e.g. outdoor reset). You probably will find that there are a number of options to improve reliability and overall life. For larger boilers parallel positioning controls, O 2 trim and variable speed draft fan controls should be considered.

Consider that more than one grade of valve is available for a given application. Some valves are designed to be repaired. Others are design to be discarded. Alternate materials of construction for the trim also affect the serviceability of the valve. If your facility is designed for 50 or more years, you might want to specify the better grade. Learn the details.

Determine how the system will be replaced at the end of its life. Ascertain paths in and out of the building. If you are evaluating a replacement project, don’t rule out retubing, new controls, or a new burner to solve problems when the pressure containing parts are fundamentally sound. And to ensure cradle to cradle, evaluate disposal, reuse, and recycling options.

After considering options for your repair, replacement, or new design, compare a few leading contenders and do a lifecycle economic analysis, taking into account first cost, operating cost (including fuel, electricity, and maintenance), and end of life disposal cost. If you are feeling brave, consider a lifecycle assessment (LCA). An LCA is the investigation and valuation of the environmental impacts of a given product or service caused or necessitated by its existence. As years go by, LCA will become more a part of the evaluation of engineered solutions.

Understanding owner’s needs and goals ensures that not only has the equipment lifecycle been examined, but also most importantly the solution provided will meet the owner’s needs.



Author Information

Scruby performs all elements of design and construction phase commissioning for mechanical, electrical, controls, and process systems as well as managing and mentoring others at Facility Dynamics.




No comments
The Top Plant program honors outstanding manufacturing facilities in North America. View the 2013 Top Plant.
The Product of the Year program recognizes products newly released in the manufacturing industries.
The Leaders Under 40 program features outstanding young people who are making a difference in manufacturing. View the 2013 Leaders here.
The new control room: It's got all the bells and whistles - and alarms, too; Remote maintenance; Specifying VFDs
2014 forecast issue: To serve and to manufacture - Veterans will bring skill and discipline to the plant floor if we can find a way to get them there.
2013 Top Plant: Lincoln Electric Company, Cleveland, Ohio
Case Study Database

Case Study Database

Get more exposure for your case study by uploading it to the Plant Engineering case study database, where end-users can identify relevant solutions and explore what the experts are doing to effectively implement a variety of technology and productivity related projects.

These case studies provide examples of how knowledgeable solution providers have used technology, processes and people to create effective and successful implementations in real-world situations. Case studies can be completed by filling out a simple online form where you can outline the project title, abstract, and full story in 1500 words or less; upload photos, videos and a logo.

Click here to visit the Case Study Database and upload your case study.

Bring focus to PLC programming: 5 things to avoid in putting your system together; Managing the DCS upgrade; PLM upgrade: a step-by-step approach
Balancing the bagging triangle; PID tuning improves process efficiency; Standardizing control room HMIs
Commissioning electrical systems in mission critical facilities; Anticipating the Smart Grid; Mitigating arc flash hazards in medium-voltage switchgear; Comparing generator sizing software

Annual Salary Survey

Participate in the 2013 Salary Survey

In a year when manufacturing continued to lead the economic rebound, it makes sense that plant manager bonuses rebounded. Plant Engineering’s annual Salary Survey shows both wages and bonuses rose in 2012 after a retreat the year before.

Average salary across all job titles for plant floor management rose 3.5% to $95,446, and bonus compensation jumped to $15,162, a 4.2% increase from the 2010 level and double the 2011 total, which showed a sharp drop in bonus.

2012 Salary Survey Analysis

2012 Salary Survey Results

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.