Energy

CHP: Innovations and Applications

The evolution of combined heat and power systems

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Steam turbine technology has been around a long time, says Tony Weidner, North American sales manager, Powergen, Elliott Group. The idea of using fuel to generate electricity and beneficial heat at the same time by recovering otherwise “wasted” thermal energy from electricity generation for other uses has been around just as long.

In fact, combined heat and power, or cogeneration, has been around since at least 1882, when Thomas Edison used a CHP plant as part of Pearl Street Station, the world’s first commercial power plant. Traditional power plants were located next to a river, lake, or cooling tower to dispense heat, but this plant was one of the first to produce electricity and use heat for thermal processes, such as warming other buildings in the neighborhood. It achieved 50% efficiency through capturing otherwise spurious heat.

The concept of using one fuel source for electricity and thermal energy endures because it’s easy to produce. “A reciprocating engine can do it,” postulates Anne Hampson, lead CHP consulting group, ICF, offering the example of a car using fuel to drive and capturing the resultant heat to warm the interior. “Different technology types can do the same process: fuel cells, gas and microturbines, boilers, steam turbines. All are very efficient at producing energy output.”

CHP technology is established, Hampson emphasizes. “It has a long history with engines.” While that has gone largely unchanged, the recent focus is on smaller system sizes. Just five years ago, there were not many in the smaller size range, but packaging techniques make them easier to install. “It’s not just for the larger energy users. Now, grocery stores, nursing homes, restaurants, and convenience stores can use them.”

Another factor driving this development centers around cost. On a per-kilowatt basis, bigger systems are still more cost-effective, but, Hampson says, “the difference is thinning” due to changes in the energy market that make renewables more accessible. “We’re getting there…and the innovation to adapt the industry to smaller sizes opens the market.”

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Fueling Around
Innovations in CHP are coming from indoor controls technology, says Jim Crouse, vice president of sales and marketing, Capstone Turbine, a leader in microturbine technology. Current microturbines featuring inverter-based output power run on air bearings that require no lube and have extended maintenance intervals as well as low emissions (because they are specifically designed to meet California standards with no exhaust after-treatment).

The high-efficiency heat recovery modules increase thermal recovery by 10%, Crouse calculates, adding that Capstone is working on programs focused on sizing and efficiency—specifically, larger 250-kW and 370-kW turbines with the potential to take electric efficiency to 40–45%.

Another change Crouse sees in the industry focuses on fuel sources. “We are pushing the envelope on fuel to include propane and butane and other fuel sources,” he elaborates. Capstone is working with the Department of Energy on hydrogen, a zero-carbon, renewable fuel. Additional fuel types being used include solar, wind, and digester/landfill gas. The latter is cost-effective for wastewater treatment plants, where it’s used to heat the digester, but some of the other fuels—particularly renewables—are driving the growth of CHP in the Pacific and Caribbean islands. Low natural gas prices also drive interest. “Natural gas is a backup source of fuel in Canada and other places because it’s reliable,” he explains.

“Renewable [energy] is collaborative, not competitive,” Crouse continues, explaining that some users generate a base load, but use solar and wind for peak load. “More customers take advantage of multiple technologies, especially if they have solar and battery storage.” Advanced controls enable the different technologies to work together. Loads, pricing, and other factors contribute to the choice of power source to use to hit the given parameters of the end-user, whether it’s for environmental benefit or economic benefit.

CHP can run on a variety of fuels, Hampson affirms: “natural gas—a fossil fuel; biogas (from wastewater treatment digesters), landfill gas, and more.” Thanks to a database of CHP systems that track applications, she sees an increase in the number of systems using biogas or other types of what she calls “opportunity fuel.” “It’s the perfect way to use waste.” With the push for renewables, there’s now a lot of renewable CHP, she adds.

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Applications
Another initiative Capstone is working on with the DOE involves the Army and the Navy, Hampson says, and concentrates on resiliency for mission critical and emergency applications. “Resiliency—having generators for onsite energy—is a major driver. Think about hurricanes and hospitals.”

In fact, it started with Hurricane Sandy, which she said was a “big jolt” for backup power. Some entities were better prepared for the recent storm in Puerto Rico; Hampson mentions one food processor that was able to keep operating because its cold storage facility never lost power.

Other typical industry customers she lists include hotel chains and grocery stores, like Whole Foods, which has a mission statement that refers to sustainable goals. “Some customers respond to a sustainable image,” says Hampson, noting the change in the way businesses see things. “It first started at colleges because of students, but it has spread. Other priorities are showing up; it’s not just economics anymore.”

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There are some surprising customers of CHP, such as companies in the oil and gas, petrochemical, and ethanol industries. They all incorporate heat-intensive processes, Weidner explains. “Anyone with steam available is a candidate.” That includes a tomato paste cannery plant in California.

There’s been more interest the last couple of years, the Elliott Group’s Weidner believes: a “push for CHP applications.” That push extends to industries such as pharmaceutical, casinos, computers, food processors, and indoor manufacturing, where power interruptions can cause damage to the products being made.

Perhaps part of the reason for that is that people are just beginning to realize that it can be an option. “The concept has been around for years, but it’s still foreign,” speculates Steve Acevedo, president and CEO of Regatta Solutions Inc. He says it’s been difficult to overcome the “disaster stories” that create skepticism and discourage adopters, and some projects have been predisposed to issues with regulatory agencies regarding permitting and air emissions.

However, Regatta’s approach demonstrates success, which is why they have completed more CHP projects in the mid-market space (1–2 MW) than any other company in California, Acevedo says. His company uses a new big-data, cloud-based company—Agave Systems—as a virtual energy manager that allows real-time access to utility bills and also provides recommendations, Energy Star reporting, and GHG reporting, which he says their oil and gas clients particularly appreciate.

Chino Valley Farms, an egg production customer in California, wanted to reduce their energy costs and improve efficiency. “Utilities are 30–40% of operating expenses for most companies,” estimates Acevedo. “They all want to reduce costs and improve efficiency.” This large plant used three co-gen stations to take the heat source to three areas, where it was used for cleaning and disinfecting. They burned the gas turbine to create heat, Acevedo explains.

Another customer used a gas turbine instead of a boiler to make hot water and create steam for its brewing processes. “The turbine is the equivalent of natural gas, and they get electricity as a byproduct,” says Acevedo.

It’s all about “chasing thermal value,” either to chill or heat. For example, an absorption chiller to create chilled water at Memorial Hospital in Los Angeles relies on a turbine to feed its water plant instead of an electric chiller, says Acevedo.

Hot and chilled water is the traditional CHP market, Crouse concurs, but it’s certainly not the only one. “Steam generators used to be large,” he explains. “Now, you can use a smaller unit.” That benefits a lot of businesses. For example, he says that the beer and beverage industry is using a microturbine instead of a boiler. Microturbines are also effective for industries that require more direct drying—for paint, bricks, cosmetics, or for food processing. “They used to use a burner; now they use microturbine exhaust.”

In addition, microturbines can help companies in the oil and gas industry with flaring issues. “We have an off-shore customer in California that uses a gas turbine to eliminate flaring,” says Acevedo, and another in North Dakota. “Turbines burn waste and stranded gas instead of flaring, which is bad environmentally, to generate electricity and reduce operating expenses.”

Installation
Installation used to be complex, but is now moving toward “appliance-level,” Hampson believes. Most buy a packaged CHP system—consisting of a generator and heat recovery system electrical gear—in a shipping container. “It’s a standard package to easily replace existing equipment in a seamless transition with little moving of pipes and retrofitting.” Customers don’t want to move pipes, she adds. They want flexibility.

Although she says most new facilities want CHP, she also believes that the majority of commercial builders put in the cheapest equipment available. It’s not always equipment that makes CHP costly; sometimes the expense is installation. “Builder standard is not usually energy-efficient, so we have to retrofit even new buildings,” says Hampson, who consults with the federal government, utilities, the Department of Energy, and the EPA on utility program implementation.

The majority of installations are retrofits, Crouse says. “There are some greenfield, new-build installations, but most are brownfield when a company upgrades. They typically improve the efficiency of the plant by adding, not replacing.”

Prepackaged systems integrate into the existing infrastructure to produce baseload or supplemental energy and average a return on investment in three to five years.

Industrial customers want a 2- to 3-year payback, while universities and hospitals want a 7- to 8-year payback, Weidner indicates. Where electricity costs are higher, the payback is even faster. Energy prices are going up as renewables are being added because of the need for additional infrastructure.

Powergen installs “a lot of new equipment,” says Weidner, much of it under 50 MW, ranging up to “a couple hundred kilowatts, and as small as 50 kW.” However, when considering the smaller units, he advises evaluating the economics because it’s more difficult to achieve a timely ROI on smaller units.

Payback period aside, installation is not a trivial process, Acevedo says. “The challenge is that the majority are retrofits.” There can be spatial challenges, which is why Regatta works with the design engineer and the architects to plan early. Even then, some issues are insurmountable. Because there was simply no space on a Hawaii hotel, and because of a Laguna Beach facility’s height restrictions on the roof, they didn’t do those projects. “You could see the gas turbine from the street. That was unacceptable.”

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PRV
Despite new fuel sources and changes in size, Weidner maintains that, “There’s not a lot new in CHP. The most recent is the pneumatic trip system on the steam turbine, which is an update on the mechanical trip valve.”

Pressure reducing valve (PRV) replacement is a recent trend. District heating, which utilizes steam to heat cities and campuses, has been around for more than a century and is still being used today. “Rochester, NY, uses district steam to heat buildings and the University of Missouri sends steam throughout the campus,” mentions Weidner.

But many industrial complexes produce steam at a pressure that is too powerful to use to heat buildings; when that happens, a pressure reducing valve is used to drop the steam pressure to the desired level. But while the PRV effectively reduces steam pressure, it also wastes valuable energy.

Elliott’s state-of-the-art steam turbine generator sets (STG) allow consumers to capture this wasted energy by placing the STG in parallel with an existing PRV. This makes it possible for the user to produce electricity as a byproduct of the system’s primary purpose (heating) safely, thereby increasing their energy independence. Elliott’s STG extracts the excess energy from the steam to produce electricity, instead of wasting it across a valve. The result not only saves the consumer money, but it also increases the system’s efficiency.

“You can generate steam from the boiler at high pressure, then run it through a turbine to produce electricity, and lower the pressure for your needs,” explains Weidner. “It makes the system better because you put electricity back into the system and recover wasted energy.” According to Elliot, steam passes through PRVs, also known as letdown valves, at various locations in the steam distribution system to let down or reduce its pressure. A non-condensing or backpressure steam turbine can perform the same pressure-reducing function as a PRV while converting steam energy into electrical energy.

The steam turbine does not consume steam. It merely reduces the pressure of the steam that is exhausted into the process header. Modern power plants with 1,800-pounds-per-square-inch-gauge superheated steam boilers and condensing turbines exhausting at near-vacuum pressures can generate electricity with efficiencies of approximately 40%. Greater efficiency means less fuel consumption.

“You’re always trying to get every bit of efficiency and energy out of every fuel source, but it’s not always a steam turbine,” points out Weidner. Gas turbines are also used. Most steam users do not have the benefit of ultra-high-pressure boilers and cannot achieve such high levels of generation efficiency. However, by replacing a PRV with a backpressure steam turbine, energy in the inlet steam can be effectively removed and converted into electricity.

Distributed Generation
Distributed generation is being used increasingly to offset utility costs if a business has excess steam, Weidner explains. It’s a move he predicts will continue…and spread. Already he sees more utilities “getting on board” with CHP. “Look at certain customers, like universities. Utilities are adopting the ‘join, not lose’ concept. That’s new.” He points out that Clemson University is leasing land to Duke Energy to build a CHP plant just for them. “It’s a way for utilities to keep customers.” The universities benefit from a better rate with no capital costs.

It’s an attractive option, Acevedo agrees, but for it to be a truly viable option, the manufacturers must have reliable systems and parts available to avoid downtime for their customers. “In California, if you have a one-megawatt gas turbine and you’re down for more than 15 minutes, you get hit with demand charges of $40,000 per month.”

Another hurdle is the cost. Although CHP saves money over time, the capital outlay—upfront costs—can be significant. However, Acevedo says, “if you remove incentives for other power sources, CHP has the lowest cost.” And, he adds, “Cheaper isn’t better.”

Regatta tries to get clients to consider blending in battery storage and solar to create a microgrid for a net-zero environment. However, they also need a commitment from the business, including a long-term plan of at least 10 years and a willingness to tell the world. Green marketing is an important competitive differentiator. “Those are the things we look for in clients.”

Ultimately, he thinks cogeneration “needs to happen.” There are too many benefits, such as reliability and resiliency, particularly when natural disasters occur…and too many areas of vulnerability in our aging infrastructure that can be bypassed and overcome by incorporating CHP. BE_bug_web

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