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Facilities Engineer Faces Boiler Choices Head-on

Selecting and purchasing equipment to supply heat and steam for essential services at Shelby Baptist Medical Center’s new $94-million South Tower and central energy plant was a big decision that required the input of many people, including engineers, contractors, facilities managers and medical-center administrators—ultimately, however, the decision fell on Facilities Director Frank Hutchinson.

The recently completed SBMC South Tower Project in Alabaster, AL consists of a new 167,712-sq-ft, four-story bed tower that houses 101 patient beds and provides additional space for other hospital services, including a surgery center, clinical laboratory, central sterile supply department, an admitting/registration area, public space and mechanical space. The new tower is powered by a new 15,000-sq-ft central energy plant with three 300-bhp Miura EXN-300SGO dual-fuel boilers providing steam for heating the tower, as well as powering a surgery center and the hospital’s central sterilization unit. But this was not the original plan.

An engineering firm consulting on the project had committed to installing three older-style 400-brake-horsepower, fire-tube units. After reading a magazine article about a hospital that had a successful installation using on-demand steam technology, Hutchinson decided to do some more investigating. This eventually led to a visit to a hospital trade show where he met Craig Simons of Marspec Technical Products (Spanish Fort, AL), who put Hutchinson in contact with the facilities director at the university hospital featured in the article. The manager at that hospital told Hutchinson of the fuel savings the new boilers brought to his facility.

“While I was checking references, I spoke with my counterpart at the other hospital [who] told me that after the first month of operation, the local gas company came by and replaced its meter because his gas consumption had dropped so much [that] they assumed their meter was broken, which it wasn’t.”
After speaking with several other users of these boilers and comparing the statements about energy use with those not using them, Hutchinson confirmed his decision.

“I looked at the engineering plan and sat down with Marspec to do the numbers. We found that only three 300bhp units were needed instead of the proposed three 400-bhp boiler configuration,” Hutchinson said. “I made them [the engineering firm] run the numbers again, and they agreed that I was right and acknowledged the projected $60,000-per-year savings on natural gas costs revealed by the calculations.”

Taking matters into his own hands, Hutchinson rejected the engineering firm’s plan and substituted three 300BHP dual-fuel boilers to replace the four proposed fire-tube units. “I really stuck my neck out on this one, but it was the right thing to do, and I’m very glad I did,” Hutchinson added.

The project
Installation of the boilers was performed by Marspec Technical products, under the supervision of Simons. The medical center’s boilers feature on-demand steam technology that employs a once-through design, which can produce usable steam output in five minutes. Compared to conventional boilers that can take up to two hours to warm up, this can translate into huge savings on fuel costs while eliminating the need for many hours of full-power operation each week.

The rapid start-up allows multiple-installation users to turn off any boilers that are not in use, eliminating the fuel expense involved in having boilers idling in standby mode. The modular design allows the dual-fuel boilers to be switched on and off to match varying load demands throughout the day. The system is able to automatically respond within seconds to increased demand and then switch to standby once the demand has been met. Since these boilers heat much smaller quantities of water, turning a boiler off results in far lower radiant losses than those that occur with fire-tube units, since their larger-volume pressure vessels have more surface area for heat to escape into the surrounding air. The rapid-start also allows boilers that are not in use to remain off, rather than idling in standby mode.

SBMC has plans to eliminate two existing 200-bhp fire-tube boilers in the older section of the hospital, and connect the older section to the newly installed central energy plant. The three dual-fuel boilers can handle the additional load without the need for more units—although the space saved in the compact design leaves room to add additional boilers should the need arise.

Hutchinson reports that his water-treatment company has already reduced his upcoming water-treatment contract by $20,000 per year to account for the loss of the older 200-bhp boilers. Also, Hutchinson said, “The new bed tower encompasses more square footage than the old hospital wing and we have moved the surgery center, cath lab, and central sterilization into the new tower as well. Even with this substantially larger load, we are seeing a 35%–50% reduction in fuel costs compared with running the old facility. And with annual fuel costs exceeding $400,000, these new boilers can pay for themselves in just a few years time.”

The dual-fuel boilers also produce fewer emissions than conventional boilers—including reduced levels of nitrogen oxides and carbon dioxide—accomplished by reducing the temperature of the boiler’s flame, which in turn reduces the amount of excited nitrogen atoms available to bond with oxygen to form nitrogen oxides.

The product
The boiler’s design consists of rows of vertical tubes sandwiched between two annular headers. Both headers are encased in a castable refractory with only the tubes exposed to flame and/or combustion gases. The upper header is attached to the lower header only by the tubes; as the tubes expand and contract, the headers float up and down accordingly. This “floating header” concept—aided by forced flow—reduces stress and allows for the use of cold feedwater without the fear of significant thermal shock.

The design also minimizes carryover and produces dry, 99%-saturated steam through a three-stage process:
1. Initial separation in the tubes;
2. Second separation in the upper header and baffle plate; and
3. Final separation in the cyclone separator.

Scale is a problem all boilers have to deal with, which forms when boiler feedwater is not properly treated. Advanced scale formation acts as an insulator; only an eggshell thickness of scale results in a 10% efficiency loss, higher fuel bills and possible damage to the boiler system. To help eliminate scale, models are equipped with thermocouples attached directly to a tube. Should scale begin to form, the boiler will alert the operator so the source of the water hardness can be traced and repaired—via an acid rinse.

The end-result
Hutchinson and SBMC are pleased with the performance of their new boilers and the savings they are achieving— savings they expect to increase when boilers in the older section of the medical center are turned off for good.

“Being placed in charge of deciding what type of boiler SBMC would rely on for many years to come was a big responsibility, which I didn’t take lightly,” Hutchinson said. “In that position, the easiest thing to do would have been to go along with the engineers’ recommendations. But, I did my own research and discovered a better solution to SBMC’s needs.”

Because of this, SBMC is benefiting from lower fuel costs and reduced use of water-treatment chemicals while the surrounding community also has cleaner air to breathe. “In my book, this is a win, win, win situation for everyone concerned,” Hutchinson concluded.

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