Bent-watertube design makes heating system shipshape
October 01, 2002
Appeared in Engineered Systems
In 2000, the Navy decided to replace the 45-year-old boiler system at its Great Lakes Naval Training Center just north of Chicago. The Navy sought newer high-efficiency equipment that offers the lower emissions required by stricter EPA guidelines and provides the improved efficiency to cut down energy consumption and pumping costs. Greater reliability, maximized safety, and increased automation to reduce operating and maintenance costs are also desires.
The center had relied on a high-temperature, hot water distribution network to heat three large warehouses, covering 1 million sq ft for housing, which contain the central distribution that serves the facility. Water was heated to 350 degrees F before being pumped through underground pipes to heat exchange equipment that connected to individual heating loops in each building. The water lost up to 100 degrees of heat as it went through the naval base and returned to a central utility plant for reheating.
No Fretting About Stress
Syska Hennessy Group Construction, Inc. (New York) was selected to coordinate the project. Jon Coleman, P.E., of that group selected the Unilux Boiler Corp.'s (Woodbridge, ON, Canada) bent-watertube design, Model ZFHTHW, based on its track record in high-temperature, hot-water installations and the low parasitic power requirements of the natural circulation of the units. High-temperature installations experience large temperature swings.
Stoermer-Anderson (Cincinnati), the equipment supplier and subcontractor, teamed with the D-B experts from Syska Hennessy to carry out the task of supplying and installing the new system while keeping the hot water plant in operation full time. A team of engineers under Syska project manager Bob Geremia spent four months onsite, renovating the existing space and installing the new equipment.
An entire wall had to be taken out to allow the removal of the old equipment and installation of the new boilers, which required a much smaller operating space. New beams were installed for structural support and a 3-ft-high pad of structural steel and concrete was installed to support the equipment. The chimney was lowered to control the draft, and engineers reconfigured the interior breeching to fit the new boiler.
Constant Operation Poses Challenge
The Unilux Model ZF1200 HTHW boilers designed for 12,500-MBtuh input and 10,000-MBtuh output, were fitted with Gordon-Piatt (Tulsa, OK) low-emissions burners to meet current EPA emissions requirements of 30 ppm NOx and CO. Keeping the existing control system in operation while the team configured the new, automated system posed a significant challenge. Critical electrical circuits had to be identified and left in service while the Unilux system was installed and commissioned. The new boilers are controlled by a supervisory control and data acquisition system that periodically checks boiler room status, temperature and pressure, turns the pumps on and off, and opens and closes the valves.
To create a system that allows the Navy to remotely monitor and control an unmanned boiler house, Syska Hennessy value engineered using constructability reviews to conceptualize the completed project. As a result, they were able to guarantee their design and construction costs earlier.
The old system required around-the-clock monitoring. An attendant had to be onsite around the clock to ensure continuous operation and to restart it in the event of a system shutdown. Mike Hoeth, maintenance engineer said, "The new boilers are checked once per shift during the heating season. These boilers are self-controlled and remotely monitored ... They virtually run themselves."
Since this project was completed in the midst of a tough Chicago winter, great care was taken to maintain continuous boiler service to the three warehouses. Engineers segregated the control system serving the old boilers so one could be taken off-line, demolished, and removed with no disruption. Demolition and removal were timed to coincide with delivery dates of the new boiler equipment. Because the older boilers contained asbestos, they had to be separated by protective barriers and abated on site without impeding normal boiler operations.
Since the new boilers were installed three years ago, the Navy reports operating efficiency has increased by 30%. Comparing these boilers to similar-sized steam boilers within the facility, Hoeth says, "Steam boilers require about $50 per day in water chemistry and [for] makeup [air] compared to the very low water consumption rates of the high-temperature, hot-water system."
Reduced electrical power consumption is also an additional benefit of the retrofit. Induced-draft fans were eliminated and pumping costs were reduced with the forced-draft natural circulation of the Unilux boilers.