More power, more efficiency: That’s the call from businesses across the globe. Whether it’s a factory that melts iron, or a city that provides district heating, all are feeling the pinch as utility costs rise. The answer for these power hungry industries is simple, use energy-efficient combined heat and power (CHP) systems. However, these systems must operate in a broad spectrum of environmental conditions and performance parameters. Manufacturers are responding to those demands with innovative products, and importantly, they are available today. Let’s take a look at technologies that raise the bar on performance, and some exciting installations that could fit your situation.
“The engine is tuned to produce slightly less electrical efficiency, in favor of the heat output,” says Patrick Frigge, general manager for GE Distributed Power. “We have a great advantage because we can tap into the intercooler circuit between the two turbocharger stages, and that gives us more total efficiency. We have an official target of achieving 95.1% total efficiency, and from our latest discussions with the engineering team, we will reach beyond that.”
By capturing the engine’s heat with an innovative design, the project demonstrates that CHP systems can find higher efficiencies by looking beyond the exhaust heat. The Hamburg project employs a heat pump installation to leverage all of the heat from the engine, even the radiant heat. “The generator produces waste heat, and typically, an engine needs to be cooled,” explains Frigge. “But in this case, we are using so much energy from the engine that we don’t need to cool it.”
By eliminating the radiator and cooling system, the engine drops the parasitic load associated with such systems.
However, Frigge credits the heat pump for the extra boost in efficiency. “The concrete building is designed so the radiant heat in the engine room is just directed to a heat exchanger connected to the heat pump,” he says. “Also, there is a duct on the generator that captures heat and it’s taken to the heat pump. It was amazing for me to see what we’re doing to reach a world record in high efficiency.” While initially targeting the segment for supporting utility operations such as Hamburg’s, the J920 FleXtra engine could find use in applications using onsite power for universities and other large power consumers.
The J920 is rated as a 10-MW class genset, but many industries and facilities have higher power requirements, and subsequently, they present opportunities for gas or steam-driven turbines. For example, if we leave Germany and head to Texas, we’ll find an installation where an aeroderivative gas turbine (the same technology that powers aircraft), supplies power at one of the world’s largest medical centers. This particular project is a CHP plant at Thermal Energy Corporation (TECO), using GE’s LM6000 PD Sprint aeroderivative gas turbine to provide 48 MW of power. The turbine’s exhaust generates steam for the physical plant at the Texas Medical Center in Houston, TX.
According to Steve Cooper, GE Water and Power, the LM6000 has a specific role in providing electricity and heat to TECO’s chilled water system and steam production plant. “It’s generating electricity that’s consumed locally within their plant,” says Cooper. “They have a focus on the economics of efficiency.
So these plant operators are getting more bang for their buck on the fuel for the gas turbine. Also, there’s a financial benefit from the heat on the backend.”
Cooper notes that gas turbines have operating parameters that can handle challenging power requirements. “In Texas, there’s some volatility in the market throughout the summer time, so this unit would run daily 24 hours,” he explains. “But on the shoulder months, when the price of electricity is lower, it may not be advantageous. The key is having a unit that’s capable of starting and stopping, so it can be ramped up and down as needed. The LM6000 has high flexibility and can start and stop daily. Of course, longer runs are better, especially when you are doing cogeneration.” Maintenance is one of the many factors that should be considered in the choice of a gas turbine, and the decision should include an analysis of the product’s lifespan and life cycle cost.
The market for large-scale turbines is expanding due to the worldwide growth in energy consumption. According to the International Energy Agency, global energy demand is on pace to rise by 33% from 2011 to 2035. Developing countries are seeing much of the demand. For example, PW Power Systems Inc., Glastonbury, CT, recently announced a contract to provide its newest technology offering, the FT4000 SWIFTPAC gas turbine to a location in FrÃas, Santiago del Estero, Argentina. It’s first FT4000 SWIFTPAC sold in Latin America.
The FT4000 SWIFTPAC is a modular electric generator package design, powered by a Pratt & Whitney PW4000 derivative gas generator and a newly designed industrial power turbine. It offers a 60- to 120-MW range of peaking and baseload power that can accommodate a range of applications, from simple-cycle, to combined-cycle, to cogeneration. PW Power Systems (formerly Pratt & Whitney Power Systems, PWPS) notes that flexibility is an important feature that allows the free-turbine design of the system to run as low as 25% of full load, using synchronous condensing operation without a clutch. On the higher end of the energy scale, Exelon Generation recently purchased a 120-MW simple-cycle FT4000 SWIFTPAC power generation unit for a power plant in Harford County, MD.
“The FT4000 is the latest technology offering by PWPS, and the first units will be delivered to Exelon,” says Charles Levey, vice president of PWPS. “It’s a 120-megawatt unit that we will be providing on a turnkey basis, so it’s two packages. One is a single-engine 60-megawatt package, and one is a dual-engine twin package. These units are 120-megawatt configuration with the simple cycle first; efficiency is close to 42%. This will be a game-changing project because of the power density, the efficiency, and state-of-the-art technology. The FT4000 is a true simple cycle, 120-megawatt, 42% efficiency machine so you have higher reliability, less capital cost, and less life cycle costs with higher efficiency. That hits all the buttons.”
The FT4000 packakge that will be supplied to Exelon is a 120-MW package supplied with a “Twin Pac” configuration where two gas turbines are connected to a double-ended electric generator. PWPS has been supplying gas turbine “Twin Pac” packages for more than 50 years.
The Exelon project will be provided by PWPS on a turnkey basis. Levey notes that the ability for an OEM to execute a project on a turnkey basis is very appealing to customers and project investors and in many respects significantly reduces the project’s risk profile.
The design of a gas turbine genset lends itself well to applications requiring mobile units. In December 2013, PWPS announced a contract to provide 20
FT8 MOBILEPAC units for four locations in Algeria. The contract also includes fuel systems, demineralized water systems, mobile self-cleaning inlet air systems, black start generators, and strategic spare components.
One MOBILEPAC unit generates 25 MW of electricity and operates on natural gas or liquid fuel. A complete power package can be shipped by land, air, or sea for rapid deployment to mitigate emergency situations in addition to longer-term solutions. The 20 MOBILEPAC units will be installed in four locations: two near Algiers, one in central Algeria, and one in eastern Algeria. The units will be delivered in support of meeting the 2014 summer peak electricity demand.
Solar Turbines Incorporated, San Diego, CA, is another manufacturer with products supporting peak electricity demand. One of the company’s most interesting applications uses three combustion turbines to provide power for a 45-MW cogeneration plant located in Mossville, IL. The cogeneration plant provides electricity, steam, heat, and chilled water services to heavy equipment manufacturer, Caterpillar, for their Mossville campus, and electricity to the company’s Mapleton Foundry.
Each of the three Titan 130 combustion turbines produces 12.2 MW of electricity, but that’s just the beginning of the plant’s energy story. It also can provide up to 410,000 pounds of steam per hour, and 7,200 tons per hour of chiller capacity. The chiller plant includes two steam turbine generators rated at 8.9 MW, a York International natural gas engine driven chiller, powered by a Cat 3412 engine and two York electric chillers. Heat from the turbines’ exhaust runs through the steam generators to heat water into steam. Caterpillar uses the steam in the winter for heating and manufacturing processes. In the summer, the steam runs through the absorption chillers to provide chilled water to cool the factory building.
The use of chillers driven by gas engines and electric drives offers a number of options for gaining higher efficiency ratings from gensets, especially with the need for cooling that coincides during a utility’s peak rate hours. A project at the Time & Life Building in New York City offers just one of many examples. The CHP system at the building has one electric-drive chiller, one steam-turbine-drive chiller, and two gas-engine-driven chillers. During summer months when rates are highest, the two gas-driven chillers take the lead. During winter, when cooling demands are low, the building facility manager can select a chiller based on the lowest fuel cost.
The proliferation of non-traditional gas categories such as biogas and syngas is inspiring new engineering solutions at OPRA Turbines, Henglo, Netherlands. The company recently introduced its OP16-3A-C, a gas turbine, designed to use three different combustion chambers. The 3A allows the use of both liquid and gaseous fuels, including diesel and natural gas. The 3B offers a low-emissions mode that can handle lean pre-mixed fuels while meeting rigid emission requirements. The 3C is designed to handle plus low energy fuels.
“The 3C is a low-BTU combustion system, so it can run on syngas, biogas, and other very lean gases,” says Fredrik Mowill, CEO, OPRA Turbines. “We anticipate seeing more lean gas applications, and we’re getting a lot of interest from the waste-to-energy industry where they have gas that is very low in BTUs. We’re also seeing projects in the oil and gas space where you’re talking about low-quality gases.”
The design of the 3A-C units is based on Opra’s OP16 turbine line and features an all-radial rotor configuration, with a 1.85-MW power output. Compared to the typical aeroderivative turbine, it has a much smaller footprint that’s beneficial to locations with limited space. Other benefits include a cantilevered rotor system that isolates bearings in the cooler areas of the engine. Engineers note that the turbine’s bearings last longer, and there is virtually zero oil consumption.
Despite the compact size of the OP16, Mowill notes that the combustion is larger than in traditional designs. “When you have low BTU gas you need bigger chambers, and we have several patented solutions for mixing the gas and injecting and cooling the combustion chamber. The rest of the turbine is identical across the three different versions so you can buy one version and retrofit it if you start using a different fuel.”
In a CHP installation, the OP16-C3 can attain a thermal efficiency of 90%. With it’s convenient size and flexible fuel options, OPRA expects to see demand for systems ranging from 110 MW, in industries such as food processing, ceramics, textiles, and chemicals. For example, SC Marex SA a food and beverage manufacturer located in Romania, developed a combined heat and power facility using an OP16. It’s connected to a co-fired waste heat recovery steam boiler, capable of up to 12 tons of high-quality steam per hour.
Steam Driven
In most CHP installations, steam turbines play a major role, and the market for this technology continues to grow across industries from food processing to iron ore production.
Of course, understanding the technology and its proper use in an application is critical. So let’s talk to an expert on the subject. David Goldsmith is an engineer with more than 40 years of experience in steam turbine technology and the owner of Greensburg Thermal LLC. Greenberg Thermal supplies heat and electricity for a local prison with a CHP system powered by waste coal as the main fuel. The facility contains one 15,000-pounds-per-hour mini ICFB coal boiler, and two 10,000-pounds-per-hour, oil-fired backup boilers. Two steam-driven turbines generate electricity for the prison’s electrical distribution systems. The system gains substantial savings by burning low cost low-grade waste coal.
“I’ve been using steam turbine equipment for the last 40 years-and not just for power plants,” says Goldsmith. “There are steam turbines and condensers for using steam to drive pumps on a tanker, feedwater pumps to provide water for motors driven by steam, and all kinds of features for mechanical drives. In all honesty, there really haven’t been a lot of technological changes in the act of driving turbines with steam, but the materials and controls have changed. Controls have vastly improved over the last 20 years due to the advent of circuit breakers and microprocessor circuit boards, so they electronically control operations much more precisely. In turn, that helps us provide more precision control for boilers to drive these the turbines.”
Obviously, steam turbines are a proven technology, but one of their greatest advantages is that they are removed from direct contact with the heat source that creates steam. So, whether the fuel is waste coal, oil, biogas, or heat from a generator’s exhaust system, a turbine system offers a wide variety of operating options, including the addition of biomass to burn along with coal. Using biomass with coal is a process that Goldsmith employs for its financial and environmental advantages. If we can diverge from the Greensburg project for a moment, let’s visit the University of Iowa (UI) to see how it benefits from adding waste oat hulls to its fuel mix.
With a peak energy load that can reach 55 MW, UI has five boilers capable of 640,000 pounds per hour of steam, and three turbine generators with 24 MW of output. There are three chilled water plants, with 18 chillers totaling 29,755 tons of cooling. Additionally, UI is one of a small number of universities that operates its own water plant. Keeping up with the annual campus demand for 855 million gallons of purified water takes 3,816 MMBtu of steam and 2,104,000 kWh of electricity per year.
When Quaker Oats offered UI its waste oat hulls, UI engineers developed a pneumatic fuel injection system that shoots the oat hulls directly into the circulating fluidized bed (CFB) of the boiler, rather than loading them simultaneously with the coal. Before the biomass fuel project, UI consumed 60,000 tons of coal annually. The university purchases the hulls at about half the price for an equivalent amount of energy from coal, thus eliminating 25,00035,000 tons of coal, and saving $500,000 annually. Those savings were based on 2004 prices. After a rise in coal prices, administrators estimated that savings increased to $700,000.
Back at Greensburg, Goldsmith uses a similar method, and tallies his cost for waste coal at less than two dollars per one million BTUs. “I’m sure you’ve heard of circulating fluid bed technology for efficient boilers,” says Goldsmith, “but most of the larger utilities don’t have those. Some independent power systems do, and they burn fuel at two dollars per one million BTUs, so we’re more than competitive.”
Staying competitive is critical to staying in business, but reliability is equally important for Goldsmith. “I’m contracted to supply electricity and steam to my customer’s 20-year contract. I’ve been operating the facility for 10 years and only had one interruption for one day. That’s more important to my customer than efficiency. From that perspective, I get turbines that work, such as the Elliott products, they have a fine record of providing a machine that’s reliable.”
Reliability is a key factor in steam turbine technology, according to Scott Wilshire, manager of power generation, Elliott Group, Jeannette, PA. Moreover, every customer’s application is unique, so it’s important to have a reasonable expectation of a turbine’s performance in a particular situation.
“Most of the time the customer knows about their steam conditions, such as the flow, temperature, and pressure,” says Wilshire. “But then they have to designate a use for the steam after the turbine is done with it. Will it be used for heating or some process? Or, will it be sent to a condenser and turned back into water for the boiler? We take those uses and look at the steam conditions, and convert their conditions into a physical model. We look at options such as a single-stage or multi-stage turbine designs, and the consequences of those choices.”
A multistage turbine has the potential to maximize the amount of electricity from the steam that’s available. “Typically, the single-stage turbines are lower power, and multi stages are higher, but there are tradeoffs,” says Wilshire. “The efficiency and output might be less with a single stage turbine, but it’s less expensive. So the customer has to look at a life cycle economic analysis, because they know all the variables that affect their business.”
If the analysis shows that a business already uses steam as part of its manufacturing process, but needs to reduce steam pressure before using it, Wilshire explains that turbines provide a power producing alternative to regulating valves. Elliott’s range runs as small as 100 kW, and a turbine that size would typically run in parallel with a pressure-reducing valve.
“If you’re an industrial manager at a district energy system, you could be producing steam at some pressure such as 300 psi, but your process only needs 20 psi,” he says. “Typically, the steam is channeled through a reducing valve to lower the pressure for process requirement, but you’re getting nothing out of that excess steam. If you put it into a turbine you get the benefit of power generation. We’ve had a number of meetings with cities in the northeast, including New York City, where the Con Ed system has around 1,800 pressure-reducing valves just in Manhattan. Think about hurricane Sandy and the grid going down, yet the steam system survived. You wouldn’t power a 75-story tower with this, but you certainly could supply backup power for many critical operations.”
Along with reliability, steam turbines are well known for their low-maintenance requirements. Other than the lubrication of bearings, yearly maintenance amounts to checking for leaks and listening for abnormal noises. A minor overhaul would involve opening up the bearings and inspecting them.
“It’s critical that they remain smooth and defect free, without contamination from foreign material,” says Wilshire. “So the bearings are inspected every three or four years. Then every six or seven years, the turbine’s blades are inspected for corrosion or erosion. If you give it dry steam and do the normal maintenance, and make sure that the oil is changed regularly, there’s no reason the turbine shouldn’t last decades. Even a 60- to 70-year lifespan is not uncommon.”
Low maintenance, a long lifespan, and substantial energy recovery, were key factors in the decision to add a steam turbine to the operations of an iron smelting plant owned by Norwegian company, Finnfjord AS. The plant produces ferrosilicon, a supplementary material for manufacturing steel and cast iron. Before adding the steam turbine system, the plant’s operations, and power hungry furnaces, consumed about 120 MW of electricity from the utility grid. Finnfjord had a goal of creating the world’s most efficient ferrosilicon production plant, and chose Man Diesel & Turbo (MAN), Oberhausen, Germany, to supply a steam turbine system.
According to Ole Hansen, head of industrial steam turbines at MAN, the star of the show is the heat recovery performance. “It’s the first plant in the world with this kind of heat recovery for this type of process, and Norway’s largest steam turbine,” says Hansen. “Previously their plant used 120 megawatts of electricity, and the heat from the furnaces just went into the air. Now, with the heat recovery boiler system, they get 40 megawatts of electricity back, and that’s a 30% efficiency boost. When they recover the heat, they have to cool the furnace, and this creates saturated steam that is sent to the recovery boiler and then used in the turbine. Simply put, it’s a utilization from the furnace and the heat recovery system. We call it a combined heat recovery system.”
Hansen notes that many businesses don’t understand how much energy is recoverable from their steam process operations. “You don’t need high temperatures or high-pressure steam to get power,” says Hansen. “We have a system in Canada where a 23-megawatt unit uses steam with power parameters of 110 degrees Celsius and 1.85 Bar, absolute. I would say that 110 degrees Celsius is more like a hot sauna. Many industries with steam of that quality just blow it out into the air. But when we explain that there’s so much energy that can be utilized, they don’t believe it; yet, it is possible.” Low-heat temperatures are common in industries such as food processing, textiles, chemicals, and paper.
With their wide tolerance for heat and pressure ratings, steam turbines have become a popular resource for renewable energy projects. For example, Alstom, a French company that builds utility-scale power plants, recently began work on a geothermal steam turbine power plant “Los Humeros III,” located in Puebla, Mexico. With an installed capacity of 25 MW, it will produce an average of more than 200 GWh per year of renewable energy.
All told, Alstom’s geothermal power projects in Mexico add up to nearly 200 MW of installed capacity. Overall, the geothermal industry is a major market for turbines. Consider that just in the US, the Geothermal Energy Association reports that there are 5,1505,523 MW of known geothermal resources under development.
With other renewables, such as concentrated solar power, using steam turbines, the future looks bright for the technology. In fact, as efficiency continues to rise for reciprocating engines, gas turbines, and steam turbines, industries that use large-scale power resources have many choices. And all of them offer the benefits of lower emissions and higher financial performance.
