By Brian Wheeler, Associate Editor

In the heat of August, Thermal Energy Corp. (TECO) completed its new 45 MW combined heat and power plant, part of a $370 million expansion of its district energy system at the Texas Medical Center, one of the world’s largest medical complexes.

With the new combined heat and power (CHP) plant, the not-for-profit service cooperative has upgraded its on-site power generation from 16 MW to 61 MW. It also now has a heat recovery steam generator producing 300,000 pounds per hour of steam for the Houston-based medical center.

Burns and McDonnell concluded the engineering design and construction for the new CHP, which is in commercial operation and providing electricity to the TECO plant and thermal energy in the form of steam and chilled water to the 18 medical institutions TECO serves in the Texas Medical Center.

The TECO generating plant (lower left) serves 18 medical institutions in the Texas Medical Center. Photo courtesy Thermal Energy Corp.

The plan to expand the energy center was developed in 2006 to address a number of items under TECO’s master plan. One was to examine the existing infrastructure in place as the 41-year-old plant already had a large chill water plant and a steam production facility. TECO had to make sure they could keep up with anticipated growth at the medical center with an unwavering goal of providing energy reliably and efficiently.

TECO President and CEO Steve Swinson said that CHP was the most efficient and reliable route to take, not only for the growth demands, but to maximize the energy system’s footprint.

“Rather than expanding like a traditional plant where you have electric chillers and gas or some solid fuel based steam generation, our expansion was planned using combined heat and power,” he said.

In July 2007, the Board approved Phase 1 of the master plan for a 75,000-ton/hour thermal energy storage tank, four 8,000-ton electrical centrifugal chillers and a 45 MW GE LM6000 PD Sprint aeroderivative gas turbine. New distribution projects, such as new piping to new buildings, cost about $60 million. In early 2008, work began and the thermal energy storage tank now has been operational for about a year, the gas turbine has been online for about 90 days and the first new chiller is scheduled to start in December 2010.

Steve Cooper with GE Energy said TECO is able to start and stop the gas turbine as needed based on changing market conditions. As the cost of natural gas and electricity change, the operation of the gas turbine can be adjusted meet TECO’s needs. While operating the gas turbine, TECO can generate steam from the heat in the turbine exhaust allowing them to reduce and optimize steam output from gas-fired boilers.

And getting the CHP system installed, along with the tie-ins, came with its share of challenges. First, the existing plant had to remain operational during the installation and tie-in due to the mission critical nature of TECO’s customers within Texas Medical Center. The Burns and McDonnell project team also worked with a tight site, which eliminated any lay-down space for equipment and forced the construction management firm to bring supplies to the site in a just-in-time delivery fashion.

“The tight site just makes everything that much more complicated whether it is safety, logistics of moving things in or the sequence of how you get it built,” said Ed Mardiat, principal in the Onsite Energy & Power group at Burns and McDonnell.

The plant, in conjunction with the south main plant, provides chilled water to 45 buildings and steam to 36 buildings at the Texas Medical Center complex. While providing energy to these facilities, the CHP plant will reduce air pollutants by 302 tons of NO_X, 305,000 tons of CO₂ and 83,000 metric tons of carbon per year.

“We are not just any site,” said Swinson. “We are serving 6,500 hospital beds and $1 billion of annually funded medical research so environmental control is extraordinarily important.”

Swinson said that electric generation in the United States has an average efficiency of about 33 percent. By using combined heat and power, TECO is able to operate at 78 percent efficiency with a combined heat rate between 5,500 and 6,700. The plant is able to produce electricity on-site and recover the waste heat to make its own steam.

“For the same energy output we are going to use half the fuel input,” he said.

The Department of Energy recently published a report showing the benefits of increasing the amount of combined heat and power generation from the current 9 percent to 20 percent of the total U.S. generation portfolio. Mardiat said that in order to take the exhaust heat off the turbine at TECO, convert it to steam and have it meet the minimum base load of the Texas Medical Center, it needs to be a large system.

“And in order to achieve the benefits outlined in the report by the DOE, new CHP installations will have be larger systems, such as the TECO system,” he said.

The facility is connected to the Houston-area grid but has the ability to operate in island mode in case of a power interruption.

“If we did have a problem and we lost grid power our emergency generator is already running so we don’t have to worry about getting it started and how long it takes to get it going,” said Swinson.

When the first phase of the master plan is complete in the spring of 2011, chilled water production will be increased by 32,000 tons due to the installation of the four new 8,000-ton chillers, an 8.8 million-gallon stratified chilled water storage tank and the 45 MW CHP plant. Future plans call for another LM6000 turbine to be installed, along with replacing the cooling tower adjacent to the substation.

The project is expected to save TECO $200 million in energy costs over the next 15 years and will increase the generating capacity by 100 MW when the final phase of the master plan is complete.