Turbines can provide numerous benefits when used for onsite power generation.
By Carol Brzozowski
In 2001, Cornell University started an energy master plan to address a growing number of concerns.
“We were faced at the time with significant load growth, the need for renewal, and deeper awareness of the environmental impact associated with greenhouse gas footprint,” says Tim Peer, P.E., Cornell University’s energy plant manager.
Cornell entered a long-term study of different options to provide heat and power, including package boilers, solid fuel boilers, and a continuance to buy power off the grid. Additionally, the university considered different sizes and configurations for combustion turbines whereby the amount of onsite generation would be increased and less power would be purchased from the grid.
“We did a 25-year discounted present value analysis Monte Carlo style. Based on that, we honed in on the Solar Titan 130,” says Peer. “We have a highly variable steam load because we have no cooling, no steam-driven turbine chillers connected to our steam load. It takes on about 400,000 pounds per hour in the winter and goes down to about 55,000 pounds per hour all summer long. The unfired output from the Titan 130 is about 60,000 pounds per hour. It nicely matched our summer load.”
Cornell has one turbine on all summer, two during the winter, and then in spring and fall one is cycled on and off.
“From an economics standpoint, the Solar Titan was a nice fit. All the power is pretty much inside the fence, behind the utility meter,” says Peer.
Cornell’s average electrical load is 30 to 32 MW with a 78% capacity factor.
“We have a very stable electric load, relatively speaking,” says Peer. “The reason why our electric load is so good is because we have no peak summer demand associated with cooling. On the cooling side, we have a deep lake water-based cooling plant that provides 20,000 tons of cooling at 2.5 megawatts. We’re next to a deep glacial lake that thermally stratifies each year. It’s like year-round thermal storage, but it’s year-round free cooling.”
In the process of choosing the Solar Turbine system, Cornell considered a small pool of manufacturers and chose Solar Turbine because the system fit the university’s need for a “strong American presence,” says Peer.
“Solar Turbine had a number of units in operation in a combined heat and power configuration and they had infrastructure in place for parts, supply and maintenance,” adds Peer. “It was a combination of their bid price, the capital costs, and how it fit into our thermal and electric profile, which translated into economic performance. Beyond that, we looked at demonstrated reliability criteria, how many units they had in the US, and how well they were supported through reference checks.”
Cornell University self-generates about 85 % of its power, with 70% of it from the Solar Titan. Beyond that, the campus has some backpressure steam turbines that are steam load following and a small hydroelectric plant.
Peer says with the amount of Cornell’s onsite electric generation, the university has complete islanding capability from the grid.
“Typically, we run parallel and we take supplemental backup power off the grid with a stand-by service from the utility,” he says. “We do have the capability to island the campus. We have tested this functionality.”
From a fuel standpoint, natural gas is the energy plant’s primary fuel. The university built a utility bypass, a dedicated high-pressure gas line.
“We go right to the interstate gas system, and we have no onsite compression,” says Peer. “We take gas at 550 psi.”
The backup fuel is ultra-low sulfur diesel, for which the university has 700,000 gallons of onsite storage capability.
“Typically, we don’t store any more than 100,000 to 150,000 gallons because we have firm transportation entitlements for gas,” says Peer. “The amount of oil we use is typically just for testing purposes. It’s a backup to the natural gas system.”
For emissions, the university does stack testing for its Title V permit renewal. Additionally, Cornell has online CEMs for NOx, ammonia slip and carbon monoxide (CO). The university is limited to 2.5 parts per million NOx with five parts per million ammonia slip.
“We do have a CO catalyst,” adds Peer. “CO is regulated 10 parts per million, but normally in operation, the CO is zero.”
Cornell has a maintenance agreement with Solar with a guaranteed availability.
“We are going into our third year of operations, and our experience with them has been very high reliability,” notes Peer. “The first few months were a little rough, but it was still pretty high. This past year—including both the turbine and the heat recovery steam generators—the availability was about 96 % availability for each unit. We were in the mid upper ‘90s.”
Solar Turbines, a Caterpillar company, offers, “numerous turbine technology advances to achieve higher firing temperatures and improve efficiency and durability,” says Chris Lyons, manager of product strategy. “Some of these proprietary technologies include advanced cooling systems and advanced turbine blade design for durability.”
Solar Turbines’ products include gas turbine engines rated from 1,590 to 30,000 horsepower, gas compressors, gas turbine-powered compressor sets, mechanical-drive packages and generator sets ranging from 1.1 to 22 MW.
Solar’s power generation packages are running in a variety of cogeneration, baseload, peak shaving, distributed power, district energy, and standby duty applications. Products from Solar Turbines play a role in the development of oil, natural gas, and power generation projects worldwide, including production, processing and pipeline transmission of natural gas and crude oil, and generation of electricity and thermal energy for processing applications such as manufacturing chemicals, pharmaceuticals, and food products.
Depending on the model, the compressors have from one to 12 stages to handle a variety of inlet flows and pressure ratios.
“Compressor sets with a single Solar compressor can produce ratios of over 5:1, while multiple, tandem-mounted compressors can produce pressure ratios approaching 40:1,” notes Lyons. “The modular component design simplifies restaging Solar’s centrifugal compressors to meet changing field conditions.”
Solar Turbines’ heat recovery systems suit numerous purposes, Lyons points out.
“One can capture exhaust heat directly for product curing and drying, heat water or industrial process fluids, produce steam for space heating, district heating, or industrial processes, and create steam to drive absorption chillers for space cooling or refrigeration.
“Combined heat and power or cogeneration is very efficient,” notes Lyons. “A customer can turn clean-burning natural gas into cost-effective, reliable electricity plus steam for production processes, heat for water and building space, or even heat to drive absorption chillers for seasonal or process cooling. It’s like getting two or three forms of energy for the price of one.
“If electricity and thermal energy are needed simultaneously, a cogeneration system can meet the requirements at a highly favorable return on investment,” adds Lyons. “Gas turbine-driven cogeneration can capture more than 80% of the energy in the fuel purchased versus 30 to 45% in standalone power production.”
Lyons points out “that by controlling a major source of electric power, you gain advantage in an industry increasingly driven by market forces, thus more volatile and less predictable than before.”
Turbine-based generation enables end users to insulate themselves against spikes in market power prices, create the opportunity to sell surplus power at a profit, and increase power reliability and lessen the risk of critical process downtime, Lyons adds.
Cogeneration is also “environmentally friendly”, Lyons points out. Operating on the least carbon-intensive fossil fuel, Solar products can provide significant reductions in greenhouse gas emissions by displacing power generated from more carbon-intensive source, while at the same time maintaining very low pollutant emissions levels, Lyons adds.
“Higher fuel efficiency reduces pollutant emissions to the air,” says Lyons. “Further, every percentage point gain in efficiency proportionally reduces emissions of the greenhouse gas carbon dioxide.
“Solar gas turbines generate clean electrical power from natural gas with power generation packages designed to limit the impact on the environment, protect people who operate the equipment, and respect people who live nearby.”
In addressing emissions regulations, Lyons points out that emissions from any gas turbine will vary by product, installation elevation, ambient temperature, type of fuel burned, and other factors.
“End users can work with a company that offers low emissions options for their turbines and have engineering teams working on new technology to address the regulations,” says Lyons.
“End users should also work with companies that have an environmental program that keeps abreast of both domestic and international laws and regulations for both new and existing equipment. Companies that invest in this resource can provide guidance on construction and operating permits.”
Most of Solar’s gas turbines include dry low-emissions technology and can meet emissions requirement nearly anywhere worldwide, Lyons says, adding the company can work with end users to meet “extremely low emissions requirements”.
Like many luxury hotels, the Four Seasons Hotel Philadelphia in Pennsylvania uses a tremendous amount of energy for cooking, heating, lights, laundry, showers, and swimming pools, among other functions.
To lower its energy costs and reduce greenhouse gas emissions, hotel management in 2009 hired E-Finity Distributed Generation to install Capstone MicroTurbines to generate the hotel’s own onsite power.
The hotel commissioned three C65 ICHP natural gas Capstone MicroTurbines, with heat recovery modules installed on each C65 to capture the microturbines’ waste heat as part of a combined heat and power (CHP) application. The return on the investment started kicking in within two months of the microturbines’ operation, when the hotel reaped $80,000 in energy savings, offering 20% less in electricity costs than utility power. The microturbines offer 195 kW of electricity, more than 1.2 MM BTU per hour of recovered thermal energy and ultra-low emissions (< 9 ppmv NOx at 15% O2). The CHP system provides 100% of the hotel’s domestic hot water needs, 30 % of its electrical needs, and 15% of its heating needs. With the system operating at 65 dB at 10 meters, it is favored for its quiet factors, something hotel guests appreciate.
“Reciprocating engines have to be rebuilt at 22,000 to 23,000 hours, have oil replaced regularly, consist of lots of moving parts, and have high vibration and noise,” says Marvin Dixon, who at the time was director of engineering. “We can’t have noise at a hotel–that would be a disaster.”
The system also provides a small footprint, with the three C65s with heat exchangers fitting into a 37-square-meter rooftop space. That was another reason why the system was selected over reciprocating technology. Prior to the C65 microturbines, the hotel relied heavily on Philadelphia’s steam loop and the local electric grid to meet its energy needs. Today, the hotel produces its own electrical and thermal power through natural gas.
Dixon says the hotel can explore various rate options by buying third-party transportation gas, making the electricity from the microturbines 20% less expensive than what could be obtained from the utility. For the commissioning, the hotel reconfigured its hydronic heating loop into a system that captures heat from the microturbines and distributes it throughout the building.
“This new process with microturbines allows for more control over heat distribution and BTUs,” says Dixon. “With such a highly efficient process, the hotel is able to squeeze every dollar out of each BTU. Instead of dumping rejected heat into the atmosphere, we can reuse it.”
|Photo: Cornell University
Cornell’s average electrical load is 30 to 32 MW.
Dixon anticipates that more hotels will utilize this technology. The Four Seasons Hotel Philadelphia plans for a Phase II installation to include two additional Capstone microturbines and an absorption chiller to meet the growing hotel’s future energy and air-conditioning needs. Turbines are built easier to operate now than ever before, points out Jim Crouse, executive vice president of sales and marketing with Capstone Turbine.
“The small turbine business has changed,” he says. “You push the start button and it starts all of the time just like it’s supposed to. The technology has advanced to the point where it’s as easy to use as an internal combustion engine. Some of the earlier barriers of 15 to 20 years ago are now gone. It’s become more mainstream.”
Turbines are not only powered by gaseous fuel, but diesel products are becoming more accepted in the marketplace, says Crouse.
Capstone is presently working on two programs with the US Department of Energy. One is a flexible fuel turbine system, designed to run on syngas.
“The challenge there is more on the generating the fuel,” notes Crouse. “We don’t have a standard fuel specification, so we’re trying to design a product to meet all of the different fuels that could come from the destruction of different materials like municipal solid waste, medical waste or tires. As that industry matures, then we can develop a product that will address the fuels that are available from that technology.”
The other project Capstone is working on for the DOE is a two-stage program in which the first stage entails the construction of a 250-kW turbine.
“We take our 200 to a 250, which will improve the efficiency and the output,” says Crouse. “The second phase of the program is to add one of our 65-kilowatt turbines so that we have one turbine feeding into another turbine with an inner cooler in-between. That will get efficiencies within the 40-plus percent range.”
Turbine end users can save money and conserve energy through accurate testing, which applies to many areas, says Crouse.
“Commissioning the plant correctly will optimize its efficiency and integration into the building,” he says. “We spend a lot of our research and engineering dollars on what we call ‘sustaining engineering’ where we’re taking the products that are more mature but continue to enhance them or keep them in compliance with regulations.”
Capstone engages in extensive testing and design changes necessary to stay in compliance with air emission regulations around the world.
“We tend to test to California standards because they’re the most stringent we’re aware of,” says Crouse. “The factor of testing is key for us to stay ahead of the curve from a regulatory and compliance standpoint, but also gives customers the confidence that our technology and products, permitting, and installation are going to be easy and straightforward.”
Sound attenuation is built into Capstone’s standard products. Standard products are in the 65-dBa range at 25 feet.
“We use air cleaners that reduce the noise from the air intake of the turbine,” says Crouse. “The nice thing about turbines is the primary noise where it comes from is fairly easy to attenuate.”
Another factor that helps reduce noise is that end users recover the exhaust energy to make hot water or chilled water “and any of those devices reduce the exhaust noise,” says Crouse.
Capstone has developed a distributed energy calculator for an iPad application. Users can determine the benefits of adding solar or wind to a CHP installation.
“The technologies are complementary, not necessarily competitive,” notes Crouse.
In the present economic environment, owners and operators are seeking cost effective ways to expand gas turbine operability, improve efficiency, gain more output and extend the life of their existing equipment, points out Mike Gabriel, product manager for turbine modifications and conversions in the Power Plant Services division of Wood Group GTS.
“The regulatory process for permitting new generation sources is slow and more demanding than ever before, thus making minor improvements to existing equipment a more attractive option,” says Gabriel.
Wood Group GTS is an energy services company that provides rotating equipment services and solutions for clients in the power, oil and gas and clean energy markets. Worldwide, these services include facility operations and maintenance; repair and overhaul, and optimization and upgrades of gas, wind and steam turbines, pumps, compressors, and other high-speed rotating equipment.
Emissions compliance is a continual focus of operating plants with the requirements becoming more stringent over time. An example is the European Union large machine directive, which is driving emissions of NOx and CO to less than 20 ppm for all plants greater than 20 MW. A similar program in the United States is driving upgrades of all non-attainment zone sited plants to the best available retrofit technology, Gabriel says.
“A lot of focus has come on power plant emissions and that’s one of the reasons why coal is receiving the pinch,” he adds. “Natural gas has become the fuel of choice with the recent increase in known reserves and the ability to obtain it inexpensively. Natural gas runs cleaner and more efficiently than coal, with up to 60% efficiency in combined cycle mode. Equipment that keeps emissions in check at coal fired plants can be very expensive to install and operate.”
Dry Low NOx (DLN) combustion systems can be retrofitted to gas turbines looking to achieve significant emissions reduction and reduced environmental impact; these systems pre-mix fuel and air prior to ignition, which reduces nitrogen oxide formation during the combustion process. Subsequent periodic testing produces information as to how the plant performs over time and may identify whether a gas turbine requires an upgrade, cleaning or maintenance to restore it to peak performance. This performance testing is typically conducted after initial commissioning and can be very expensive and time-consuming, says Gabriel.
“Gas turbine performance monitoring software enables a facility to monitor performance in real-time,” he adds. “Gas turbines are typically tuned manually for acceptable average performance at current or planned future operating conditions; however changes in ambient weather, fuel quality, and equipment integrity often impact the combustor’s tuning.”
Wood Group GTS’ ECOMAX automated performance monitoring solution continuously optimizes combustor dynamics while maintaining NOx and CO compliance and provides the ability to increase power output, Gabriel says.
“The system is set up to shift the tuning of the combustion process on demand with a simple human interface based on operational goals,” he says. “This technology continuously optimizes power output, emissions and combustion dynamics year round, while eliminating the need to utilize manual combustion tuning approaches that leave untapped capacity and efficiency ‘on the table’.
“Automatic turbine monitoring is a good way to see the performance of your gas turbine in real time and allows you to see a trend over time,” adds Gabriel. “It can notify you when it’s time to take action to correct any immediate issues as opposed to being forced to install new equipment and schedule an additional and unexpected performance test.”
Additional challenges arise from the current trend of having frequent variations in fuel quality and composition. The results can be flame-out turbine trips—lean blow-outs of the combustion system, and emissions violations as well as combustion dynamics excursions.
“These negative events are more prevalent in lean, pre-mixed, DLN combustors,” says Gabriel. “Continually tuning a combustion system can enable the turbine to successfully operate with much broader fuel composition variations.”
This can also be turned into an economic advantage for the plant, allowing consumption of lower BTU content fuel at a significant cost savings, he adds.
“Essentially, why pay for ‘high test’ if your turbine can run on ‘regular’ without ill effects?” says Gabriel.
Wet injection technology, a solution that preceded DLN, injects water or steam to reduce emissions.
“In some cases, a complete DLN upgrade may not be necessary,” says Gabriel. “A water injection system could prove to be more economically viable.”
In addition to DLN upgrades, water injection technologies, and gas turbine monitoring, compressor cleaning is vital to optimizing the operational performance for gas turbines, says Gabriel.
“Routine compressor washing is essential to maintaining turbine output and efficiency,” he says. “Significant performance degradation is usually experienced due to dirty compressor blades, especially if the gas turbine is in or near an industrial environment. Compressor cleaning can take place online with the unit in operation, as well as offline or while the engine is down.”
An online compressor water wash system significantly reduces degradation between offline compressor cleaning cycles, says Gabriel. This translates into improved efficiency and a significant fuel savings over time, providing a strong return on investment for the owner or operator, he adds.
“A common challenge for power generation turbine operators has been the need to increase the efficiency and output of their gas turbines while maintaining them in optimal operational condition—an imperative for extending the lifetime of their units with a direct impact on their capital investment,” says Gabriel. “The return on investment that an operator can receive by installing an online water wash system has been seen in less than three months in some cases.”
Like sound attenuation, emissions and fuel storage or conveyance, testing plays a critical role in the optimal performance of turbines. ComRent specializes in load bank rentals and is involved primarily in mission-critical situations in which if there is a power loss, there is going to be a significant negative impact to a company’s operation. Load bank testing is the most flexible testing method to validate the operating condition and output of diesel and gas turbine generators, says Terrence Whalen, a regional sales manager for ComRent.
ComRent’s scope includes load bank testing during a new plant installation as well as after significant improvements have been made. Past projects have included changes such as new relays, upgrades to motor controls, or increasing a plant’s size or efficiency. Testing with load banks provides a “real life” scenario of how the plant will operate before being grid tied or isolated without jeopardizing plant operations. ComRent has been involved in more than 30,000 commissioning projects and focuses on providing medium voltage load banks.
“We will provide leading and lagging power factor load bank systems, full load pickup and full load shed capabilities, and additional load to test above nameplate ratings when customer’s test requirements call for it,” says Whalen. “These rigorous exercises put power systems to the test.”
“Some of our customers rely on additional services to streamline their projects,” adds Whalen. “Those services include full logistical management, equipment placement, cable roll out and roll up, and operation of load banks at the customer’s direction.”
One of ComRent’s customers is a refinery that used the company’s equipment to test their solar turbine cogen system after upgrades to new controls to ensure proper load sharing.
“Testing has shown how close their cogens were to dropping their field,” says Whalen. “Consequently, we have done several projects with them.”
The result of not testing can cost millions in lost production, Whalen adds.
Mike Bartels, who provides inside sales support for ComRent, says the company has seen end user’s test requirements that include full load drop and full load pickup as well as black start tests.
“When a plant has to quickly take on a large amount of load, the turbines can be put under a lot of stress,” says Bartels. “Customers have asked us to provide full load pick up and full load drop capabilities to prove that their plants will quickly accept the additional load while staying within certain parameters and specifications.”
Load testing helps give customers a better idea of their cogen facilities’ capabilities, Bartels adds.
Turbine Marine’s product line includes 1450 to 1850 hp gas turbine-powered race and pleasure boats, and industrial equipment, including portable generators, high-volume fire and water pumps for emergency management, and the powering of frac pumps for the oil and gas industry.
A smaller and lighter footprint is another advantage, says John Arruda, the company’s president.
“In use for many years, these engines are reliable, durable and very easy to operate and repair. They are multi-fuel capable, including diesel, gas, jet A, ethanol, and a variety of biofuels. The latter makes them environmentally friendly and potentially inexpensive to operate.”
“They have a low down time for hot end inspections and an engine replacement can be done in under eight hours,” he says. “Additionally, the turbines have a ‘black start’ capability with load acceptance within 60 seconds. This makes them a good choice for standby and emergency applications. They also have the versatility to run as simple cycle, recuperated cycle, or cogeneration, making them energy efficient.”
Author’s Bio: Carol Brzozowski writes on the topics of technology and industry.