by Ed Ritchie
On-site CHP plants deliver a series of economic and environmental benefits to their users. However, as the recent US hurricane season illustrated once again, the ability of an on-site generation plant to keep essential power loads supplied is an equally valuable benefit to many facility operators. Ed Ritchie reports.
‘Before it was all controlled by the utilities, but right now we are seeing a lot of shifting and changing by policymakers to give more freedom to distributed generation’, says Louay M. Chamra, professor and interim head at the Department of Mechanical Engineering, Mississippi State University.
‘A hospital running on power fed from the grid would use 255% more energy than this CHP system,’ commented Ed Mardiat, principal at Burns & McDonnell Engineering Company.
The landscape for CHP in the US is changing rapidly — there is accelerated growth due to costly financial losses inflicted by grid instability and natural disasters, such as the recent round of hurricanes that swept the Gulf coast areas. Adding to the pressure are State and Federal mandates to reduce carbon emissions and other pollutants, and finally, soaring fuel costs. To win in all these areas, an installation must be able to disconnect from the grid, and operate in ‘island mode’. It’s a choice that requires a higher investment, but the following stories show just how fast that investment can pay off, with dividends.
With typically high demands for stable electricity, plus heating and cooling, hospitals and universities with critical research facilities have always been prime candidates for CHP. The Northeast blackout of 2003 and hurricanes Katrina and Rita in 2005 provided an urgent wake-up call to institutions that weren’t ready to consider the benefits of cogeneration. Many administrators changed their priorities when the blackout darkened much of the Northeastern and Midwestern United States, and Ontario, Canada, yet a CHP installation at the Montefiore Medical Center in New York City stood out for making the site the only hospital in NYC that continued to operate with full power.
The hospital runs a Taurus 60 generator set to drive a 14 MW cogeneration plant, and all critical loads are backed up by emergency power generators.
More examples of similar CHP systems that stayed online include: Entenmann’s Bakery, Bayshore, NY; Norwalk Hospital, Norwalk, CT; Pharmaceutical Plant, Rochester, MI; and the Spring Creek Towers’ offices, Brooklyn, NY.
COPING WITH HURRICANE-INDUCED OUTAGES
The wisdom of CHP was demonstrated again in 2005 when Katrina and Rita ripped through the Gulf region of the US. ‘After Katrina, people are paying much more attention to distributed energy,’ says Louay M. Chamra, professor and interim head, Department of Mechanical Engineering, Mississippi State University. ‘So we have many industries looking at distributed generation — as either completely independent from the grid or as some type of hybrid system which can operate during the day on CHP and distributed generation, then switch back to the utilities at night when the rates are lower.’
One of Chamra’s favorite comparisons when he speaks at industry conferences is the success of the Mississippi Baptist Medical Center, Jackson, MS, and the failure of the Memorial Hermann Baptist Hospital, Beaumont, Texas.
As the grid became unstable during hurricane Katrina, the Mississippi Baptist Medical Center shed some load, disconnected from the power grid, and continued in turbine-only mode. The hospital ran for more than 50 hours, and it was the only such facility in the Jackson metro area to remain nearly 100% operational. The system uses a Solar Centaur H Model natural gas turbine generator set, waste heat recovery boiler, economizer, and two double-effect steam absorption chillers. It provides 80% of total electrical needs, 95% of steam demand, and 75% of cooling needs.
When hurricane Rita followed shortly after Katrina, the Memorial Hermann Baptist Hospital at Beaumont, Texas, did not fare as well. Before Rita made landfall administrators shuttered Hermann and evacuated patients. When the hurricane hit the area and knocked out the power, the hospital’s back-up generators started, but couldn’t power the chillers or sustain operations over the length of the blackout. Seven days later, Hermann had acquired power from 22 natural gas engines, but the hospital had incurred more than $30 million in damages and lost business. Repairs took three months.
‘These two stories are perfect examples of the benefits of running CHP in an island mode,’ says Chamra. ‘More people pay attention to this issue now and they have CHP policies within the state of Texas and sustainable renewable power related to CHP. Here in Mississippi the Governor has a task force to establish a renewable portfolio and distributed energy. Before it was all controlled by the utilities, but right now we are seeing a lot of shifting and changing by policymakers to give more freedom to distributed generation.’
Ed Mardiat, principal at Burns & McDonnell Engineering Company, agrees that utilities across the US have a reputation for being less than accommodating to distributed energy. His company is currently providing architectural, engineering, procurement and construction services, and guiding for two on-site cogeneration projects that are owned by utilities.
ON-SITE, UTILITY-OWNED GENERATION
The first is for the Shands HealthCare Cancer Hospital located in Gainesville, Florida, where Gainesville Regional Utilities (GRU) is finishing a new energy centre that will provide on-site electrical power generation, chilled water, steam and medical gases to meet 100% of the Cancer Hospital’s needs in the event of an outage.
Housed in a three-floor 40,500 ft² (3800m²) space, the initial design provides 5 MW of power, 30,000 lbs/h (13.6 tonnes/h) of steam and 4,200 tons (4300 tonnes) of chilled water. The combined heat and power system uses a 4.3 MW natural gas fired recuperated combustion turbine, with a simple cycle heat rate efficiency of 38% and guaranteed NOx emissions of 5 PPM without after-treatment. A heat recovery steam generator (HRSG) produces 14,500 lbs/h (6.6 tonnes/h) of steam without supplemental firing, and duct burners will provide an additional 30,000 lbs/h (13.6 tonnes/h) of steam at a nominal 98% thermal efficiency. The chilled water system uses two 1500 ton (1520 tonne) electrical centrifugal chillers and one 1200 ton (1220 tonne) steam turbine centrifugal chiller.
Ultimately, the GRU Energy Center will provide for a future expansion of the Cancer Hospital. This includes electrical power, chilled water, steam and medical gases for approximately 3 million square feet (278,700m²), or the equivalent of 25 MW of on-site electric power, 16,000 tons (16,260 tonnes) of chilled water, and 3 MW of steam.
The estimated construction cost of the GRU Energy Center is about $35 million, and though that may sound like a high price tag, the system saves money and can even earn money in some circumstances. For the savings, the system is targeting a 75% efficiency rate of primary fuel to useful energy. ‘That’s a 46% savings compared to the typical hospital power service model,’ says Mardiat. ‘A hospital running on power fed from the grid would use 255% more energy than this CHP system.’
As for potential earnings, the turbine runs 24/7, which allows for exporting power to the grid. ‘In the event that market conditions are favourable the power could be sold at a higher rate so the hospital could have an economic benefit from the power going to the grid,’ Mardiat notes. ‘Also, in the event of a hurricane approaching, they don’t have to wait for the grid to drop out, they can isolate themselves prior to a disaster.’
The same benefits apply to the upgrades taking place at the Texas Medical Center (TMC) in Houston, Texas. Thermal Energy Corporation (TECO) operates the chilled water district energy system serving TMC, and currently provides thermal energy utility services to 18 customer-owned institutions on-site. TECO’s system has two thermal utility plants with a combined capacity of 80,000 tons (81,280 tonnes) of chilled water; 762,000 lb/h (346 tonnes/h) of steam, and a direct-buried distribution system of over 35 miles (56 kilometres) of piping, serving over 15 million square feet (1.4 million m²) of space, or approximately 75% of the facilities within the Texas Medical Center.
Mount San Antonio Community College, Walnut, California — exterior of the main plant room. Source: Chevron
With peak load increases projected at 30% in the next five years, and 100% in ten to fifteen years, TECO launched a CHP system expansion — to add capacity, improve efficiency, reduce emissions, and strengthen reliability and emergency operating capacity. Most significant is the additional combustion gas turbines generating 100 MW of on-site electrical power. The turbines will supply heat for steam generators, and the project also includes a 6 MW back-pressure steam turbine generator unit, 152,000 ton-hrs of chilled water storage (16,000 tons, 16,260 tonnes), 80,000 tons (81,280 tonnes) of electric motor-driven chillers, and the removal of one older boiler with significantly higher air emissions rates.
Mount San Antonio Community College, Walnut, California — two engine generators at the heart of the CHP system. Source: Chevron
‘By the utility owning and operating the plant many of the traditional barriers go away,’ says Mardiat. ‘In the case of TECO they will own and operate the CHP system, but 100% of the power and thermal generation will be used within the confines of the plant. Since Texas is a deregulated market they will only export when market conditions warrant that. The system is really being designed so power can be used 100% within the fence. In the event of a major grid outage TECO has the ability to disconnect from the grid to keep their plant up and running.’
Mount San Antonio Community College, Walnut, California — two engine generators at the heart of the CHP system. Source: Chevron
SWITCHING TO ISLAND MODE
Disconnecting from the grid is also one of the top reasons many universities and colleges are adopting CHP systems with island mode capability. At Mt. San Antonio Community College in Walnut, California, administrators wanted relief from utility surcharges and blackouts, plus the security of on-site power because the college is designated as an emergency disaster centre. ‘We have about 65,000 students and on any given day there might be 20,000 people here on campus — and from my perspective as being responsible for an emergency event — we need the ability to keep operating in case Edison’s grid goes down,’ says Gary Nellesen, the campus director of facilities. ‘We don’t quite have the same needs as a research university but we do have a lot of power shutdowns, five to six a year, caused by failures in Edison’s system which happens periodically, or system failures because portions of our grid are aging.’
Variable frequency drives are part of the energy efficiency measures installed. Source: Chevron
According to Gregory Coxsom, lead project manager for Chevron Energy Solutions, San Francisco, Edison was billing the college at the utility’s interruptible rate and had blacked out the campus a number of times. ‘That meant administrators had a choice of sending students home or paying enormous fees,’ Coxsom recalls. Chevron solved the problem with a cogeneration system built around two 750 kW internal combustion engines running on natural gas. The CHP system was integrated with an energy-savings program that included removing two existing eutectic salt thermal energy storage systems and replacing them with ice storage systems. Additionally, Chevron installed a campus-wide Direct Digital Control Energy Management System, plus lighting upgrades and retrofits. Savings for the first year of an 11-year guaranteed energy savings contract were almost $700,000.
The Solar Taurus turbine — part of the CHP plant at Kent State University, Ohio. The plant operates as a buffer to outages and sags in the grid.
Nelleson notes that the cogeneration system is a major contributor to keeping energy bills flat for the six years it’s been in operation. ‘This year was the first year we saw prices creep up while the campus has been growing at a rate of 9% average per year and that’s huge for a college,’ Nelleson adds. ‘We have done some other energy savings but the CHP is a major contributor.’
The first phase of a CHP system at Kent State University in Ohio paid itself off in about 18 months — but economics weren’t the first consideration in purchasing the system. ‘We were looking at deregulation many years ago and starting to have concerns about reliability,’ recalls Thomas Dunn, director of campus environment operations. ‘There was no economic reason for the decision outside of whether we could afford to add the controls that would make it happen. But we were able to accommodate that cost because the payback on the turbines was pretty good and we were able to meet our objective of paying them off in seven years.’
The first phase of Kent’s system began in January 2003, with the installation of a Solar Taurus 60 dual fuel (natural gas/fuel oil) turbine generator rated at 5.2 MW. It feeds a waste heat recovery boiler (capable of 27,000 lb/h or 12 tonnes/h of steam). Supplementary heat can boost capacity (up to 100,000 lb/h or 45 tonnes/h), as well as redundancy for steam production into the university’s main distribution system for building heating and cooling use. The second phase included installation of a Solar Taurus 70 for a total increase from 5.2 to almost 12.4 MW.
This second generator is a peaking unit and allows Kent to run independently from electric utility distribution. Kent is a 14 MW peaking campus, with typical electrical demand of 10—11 MW. It’s a good candidate for combined heat and power due both to the need for stability and the year-round demand for substantial quantities of steam.
‘We haven’t had a catastrophic failure with the need to run on our own yet,’ notes Dunn. ‘But we have had several sags in the grid over the years and the turbines have been able to ride through them so the university hasn’t seen a dip in voltage. The turbines are operating to protect us — as a buffer to outages and sags on the grid.’
As with many such systems, Kent’s turbines can be set to ‘trip off’ in the event of grid failure. ‘If for whatever reason we were to start to feed the grid the control system will literally disconnect the breakers and shut itself down,’ Dunn explains. ‘The turbines are internally protected with several protection schemes for voltage variations, frequency response, and other issues.’
If the turbines trip off it can take up to 40 minutes or more to restart in island mode. Dunn can stop the process at any time or transfer to the utility once it returns online without shutting down again. The campus has a one MW diesel generator in the CHP plant with another 50 emergency generators spread throughout campus buildings. Dunn can also use the generators for load shedding.
CHP — A MULTI-BENEFIT OPTION
Such options are becoming more common with CHP systems and — as demonstrated by the cogeneration plants that kept their facilities running through grid failures and hurricanes, security and stability are key benefits for implementations that can disconnect and operate independently of the grid.
Cogeneration also shines when it comes to fuel efficiencies. Rates in the 70%—80% range are common. Moreover, higher performance means less fuel used per watt or BTU, and obviously, less emissions. However, the benefits don’t stop there.
The GRU Medical Center provides a significant comparison of the environmental benefits available with a CHP system. The GRU’s legacy fleet of central power plants had emissions of CO2 at 1937 lbs/MWh (880 kg/MWh), SO2 at 8.44 lbs/MWh (4 kg/MWh), and NOx at 4.02 lbs/MWh (2 kg/MWh). The new CHP plant has reduced the emissions to CO2 at 615 lbs/MWh (280 kg/MWh), SO2 at 0.003 lbs/MWh (1.4 g/MWh), and NOx at 0.043 lb/MWh (20g/MWh).
Such improvements complete the picture of CHP systems as an on-site power resource that offers some of the lowest levels of emissions with the highest levels of performance, security and economy.
Ed Ritchie writes on energy matters from the US.