Innovations in Engines and Emissions Control

June 10, 2014

When skiers in California use their iPhones to text their friends at the lodge, their message may get a boost from renewable energy. Takayuki Koizumi, vice president of marketing & business development with Urban Green Energy, says his company worked with Verizon wireless to install a supplemental wind power system at a cellular tower in California ski country. The site and many like it exist far from the electrical grid, forcing the companies who own them to use onsite power generation-traditionally from diesel or propane generators. During the winter months, this can be a particular challenge. Snow buries the path out to the tower, rendering site access for maintenance or refueling nearly impossible. Before the company installed wind power, Koizumi says, Verizon crews reaching the site during the spring typically found the generator’s fuel reserves nearly empty. After installing the small turbine, though, he says the spring technicians found the tank half full-saving Verizon both money and diesel emissions.

As academics and the public at large gain a better understanding of global warming and air pollution, businesses face growing pressures to clean up their exhaust. Groups like the Carbon Disclosure Project have urged firms to take a full accounting of their supply chain carbon impact, and have succeeded in getting nearly 3,000 of them to do so. At the same time, national, state, and local governments have drafted increasingly stringent limits on businesses’ airborne externalities-which can include carbon emissions, particulate, noise, and other kinds of pollution.

In this environment, renewable power has become more attractive. Green energy remains more expensive than traditional energy sources, but the equipment is improving and it can help businesses address other challenges. It not only helps companies deal with looming regulation, but it can help polish their green credentials and reduce their reliance on fossil fuels-the prices of which remain ever volatile. In some cases, green energy can even help businesses dispose of their waste.

The Way the Wind Blows
Beginning in 1978, congress has encouraged utility companies to use renewable energy where possible and appropriate. Those requirements ramped up after passage of the Support Renewable Energy act of 2010, and have notched up regionally as states have introduced requirements for energy companies to include renewable power in their portfolios. By 2012, 30 US states had outlined standards requiring power companies to include renewables in their energy mix, and seven more had set up goals for their utilities.

Credit: iStock/jntvisual

At the same time, states have instituted increasingly strenuous standards on gas and particulate emissions allowed by firms that generate electricity-which can impact any firm with onsite generation, not just electric utilities. In California, for instance, the ports of Los Angeles and Long Beach made large-scale changes to their operations after a collection of legal and regulatory decisions forced the ports to reduce their diesel emissions. Among other changes, the ports created infrastructure and incentives for docked ships to draw power from the local electrical grid instead of running their engines to generate electricity.

The same kind of forces can impact data centers, warehouses and distribution centers that have backup power onsite. In many cases, notes Bill Clary, managing director at Miratech, state regulations don’t limit a site’s actual emissions, but their capability to create them. This means that, in some cases, a datacenter with backup generators expected to run for no more than one day per year will face the same restrictions as a production facility that plans to run its generators constantly.

These regulatory regimes have combined with a growing global movement for companies to disclose their environmental impacts-particularly their carbon footprints-to give companies a nagging incentive to clean up their energy mix. For some, this could mean installing newer, cleaner natural gas generators or installing new filters for their existing generators. It could also mean adding distributed renewable energy to their facilities.

The Windy City
The word “wind turbine” typically conjures images of enormous, 10-plus-story tall structures like the Siemens SWT-2.3, the likes of which often cluster together in wind farms that populate otherwise-empty areas. These behemoths have no place in urban centers, as they simply require too much space. But firms like Urban Green Energy have increasingly brought wind technology down to smaller, distributed scales. Urban Green Energy’s corkscrew-shaped turbines stand no taller than 35 feet, and its smallest turbine is less than four feet tall. These devices have been installed on rooftops and other high places ranging from the San Francisco Civic Center to locations around Texas A&M’s Corpus Christi campus.

While turbines are moving into territory once reserved for solar, distributed wind firms don’t necessarily aim for their turbines to replace photovoltaic cells. “Wind and solar play really nicely together,” says Russ Woolsey, vice president of marketing with Xzeres Corp.

The two pair, he says, because they tend to offset each other. Sunny hours tend to have still air, Woolsey says, while cloudy and dark hours tend to lend themselves to higher winds. Both also lend themselves to remote operations. Woolsey says Xzeres’ equipment has been popular for cellular towers in developing countries where diesel for generators sometimes has to be flown in by helicopter. His equipment has also been installed in remote villages in Alaska, and Woolsey sees business applications for wind/solar combinations at oil fields in North Dakota. (The state’s recent oil boom developed so much faster than its infrastructure that an 18 year old made a small fortune by driving a tractor-trailer full of showers to work sites.)

For more traditional, urban businesses, the turbines can function as a highly visible carbon offset. On average, every kilowatt-hours of electricity used in the US generates 1.22 pounds of carbon dioxide, compared to an in-use emissions factor of zero for wind energy.

However, these installations may not make financial or environmental sense in all cases. Lawmakers allowed a federal subsidy for wind power to expire in December, and it may or may not return in the near future. However, many states still offer wind subsidies-particularly, Woolsey notes, Oregon and New York. In other places, such as the windy midwest, installations may make financial sense even without subsidies.

Gut Check
Farmers in many states and the southern portion of Canada have seen fit to lease portions of their land to large-scale wind-installations. But they have also found another source of green energy on their land: manure. Chris Nagle, general manager with Dresser-Rand’s Power North America division, says his company produces engines that run off of gas from anaerobic digesters. The digesters take organic waste, such as manure, and convert it into useful byproducts. The digesters keep the waste in an oxygen-free environment with microorganisms that eat it and expel nitrogen-rich fertilizer, carbon dioxide, and methane. While the last of these is a powerful greenhouse gas-20 times more powerful than carbon dioxide-it can also be burned to power a generator.

For farmers-particularly dairy farmers, Nagle says-these systems solve several problems at once. In addition to producing energy, the digesters convert waste into useful fertilizer, and they keep neighbors happy be minimizing offensive odors. His company has also supplied engines for similar systems at breweries and large wastewater treatment plants.

As the regulatory environment changes, digesters may expand into new niches. In 2013, Massachusetts’s regulators announced a ban on sending commercial food waste to landfills. The state also promised accompanying subsidies to ensure that food waste could instead be sent to anaerobic digesters. Should the Massachusetts plan gain national traction, anaerobic digesters could become a “must have” for large-scale food waste producers such as universities and grocery store distribution centers. Not only would onsite digesters help these companies comply with the organic waste bans, but it could also reduce their emissions.

Dresser Rand and other companies aim to use a similar approach at landfills and natural gas fields. Both naturally emit methane, which must be disposed of for global warming reasons. Often, the methane is simply burned away or “flared.” In some cases, Nagle says, these flares stand just yards from generators that run on trucked-in diesel fuel instead of the abundantly available onsite methane.

Mixing It Up
While small, distributed green energy installations can make businesses feel good about themselves and improve carbon footprints, larger-scale installations come with a special set of complications.

Clary with Miratech says that large-scale wind farms have actually created demand for his company’s natural gas generators. Due to utility companies’ need for stability, large-scale generation facilities often sign contracts that guarantee fixed, constant energy output. Given that wind is neither constant nor fixed, this requires wind farms to supplement their renewable generation with more reliable fuels.

“As renewable energy has increased, so has the demand for what we call peaking power generation,” says Charles Levey, vice president of sales and marketing with PW Power Systems. Natural gas has become the default choice for these supplemental power installations, Levey says, because it has the best “turndown ratio.”

This means that natural gas generators work well in partial load conditions. “They [also] have the ability to start up and generate power very quickly,” says Levey.

On and Offsite
For businesses that can’t install renewable energy onsite, large-scale wind farms serving major utilities can work on their behalf. Utilities in many states allow electric customers to specify that they would like to be supplied with “green” power. What this means is that the business pays a small premium-usually a few cents per kilowatt-hour-to help pay for the utility’s renewable power infrastructure. The same option, it’s worth noting, is available to many residential customers.

While the business doesn’t directly install or operate any generation equipment, paying this premium allows the company to act as if it does. It can claim to use renewable energy in marketing materials as well as in its carbon disclosure reports. It may not have the rhetorical punch of showing that the company has installed a turbine or solar panel, but the impact on environmental accounting is the same.

However, this solution does not help businesses that need the capability to operate off of the grid in the case of power outages. Datacenters and hospitals, for example, need a constant stream of power to prevent their operational disruptions. By its very nature, renewable energy isn’t up to this task, leaving companies with mission critical energy needs to choose between diesel and natural gas.

While diesel has been long dominant for emergency operations-the generators themselves tend to be less expensive-natural gas has been gaining ground. “Some of the new natural gas engines are closing the gap quite a bit,” says Miratech’s Clary.

Natural gas also has the advantage of not requiring storage and generally performing better on emissions-though rich and lean-burn natural gas engines have significantly different emissions profiles. Lean burn natural gas engines more efficiently burn the fuel and therefore produce more energy and less nitrous oxide (NOx) per unit of energy. In many places, lean-burn natural gas engines can stay under emissions limits with no additional filtering and processing.

In places where lean-burn engines don’t meet emissions requirements, businesses may be better off with a rich-burn generator. While rich-burn engines are less efficient, their hotter exhaust allows for easier catalytic cleaning and filtering. “In some cases, idle is hot enough to keep the filter clean,” says Clary.

More About Mono Nitrogen Oxide Emissions
Where gas turbines power electrical generation, turbine health must be watched over carefully. Eric Yax with IMI Sensors, a division of PCB Piezotronics Inc., explains that the production of NOx emissions occurs in the combustion process of the gas turbine, and worldwide emissions regulations bring their own set of challenges to maintaining turbine function.

As touched on in the section above, NOx emissions are kept low by burning leaner fuel mixtures; using lower combustion temperatures helps too. However, Yax says, “This combination can lead to combustion instability. This instability can damage components in the combustion chamber such as nozzles, baskets and transition pieces, as well as downstream components, such as blades.” The damage invariably results in downtime, loss of production, repairs and “a breakdown of one turbine component, such as a blade, has a domino effect on many other parts” he says.

Turbine operators who utilize NOx emission reduction strategies use various condition monitoring techniques, he says. These tend to be dynamic pressure measurements that provide early warnings of conditions that can lead to excessive pulsations and cause instability.

“At one time these were used to trend data and accurately identify potential faults before any serious damage could occur, but now predictive maintenance is practiced as a necessary condition, driven by emissions reduction,” says Yax.

Piezoelectric sensors that monitor combustion dynamics come in one of four forms:

  1. Remote sensors to measure pressure, either portable or permanently installed-these tend to be low cost.
  2. Close coupled sensors, which have higher accuracy and precision pressure sensing; hence, these are higher cost.
  3. On-turbine instability sensors that are mounted directly on combustors-while the highest cost, these are most reliable.
  4. High-temperature accelerometers that measure vibration and withstand temperatures up to 1,300°F

“Bottom line, reduction in NOx emissions is required to comply with the environmental legislation worldwide. Therefore, since it causes combustion instability, which results in machine breakdown, it’s imperative to have a condition monitoring program to ensure trouble-free operation, prevent catastrophic failures, unscheduled downtime, loss of productivity, and even worker safety,” says Yax.

Noise Pollution
While companies must worry about greenhouse gas emissions, noise emissions can also pose a problem. Construction companies must observe OSHA-imposed noise regulations to protect workers’ hearing-particularly on small city lots where nearby buildings may reflect the noise back.

A change in practices generated by the aftermath of 2013’s Hurricane Sandy also changed the environment for generators, Clary notes. Prior to the storm, businesses tended to keep their generators in basements where the earth muffled the noise. After floodwaters filled those same basements and rendered generators inoperable, Clary says, building managers started moving generators above sea level.

Sometimes this meant the roof. Sometimes this meant a position on the second floor. In either case, he says, generator noise now became an issue. Even in very rural areas, noise can pose a challenge because unusual geological structures and thermal patterns can cause noises to travel long distances.

In response to these challenges, Clary says, designs have begun pointing exhaust directly into the air, reducing the acoustic blast on nearby ears. Generator manufacturers have also designed tighter, acoustically lined enclosures and attached acoustic muffling to the machines’ air intakes. Clary says Miratech has debuted a new design that can decrease generator noise by 60 decibels.

“In some cases the engines are quiet enough there’s no way to actually measure how effective the silencer is,” says Clary.

In a city environment where the company’s 60-decibel silencer has been attached to a 110-decibel generator, Clary says the generator is often quieter than the background noise of cars and pedestrians.

Conserve Energy and Carbon
While advancements in traditional and renewable power sources can help reduce emissions, few measures are as effective at reducing greenhouse gasses as reducing electricity use. In some cases, bridge power sources have helped with this. Clary notes that it used to be common for facilities that need a constant stream of energy to turn on their generators any time a storm approached. If the storm knocked out the grid, he notes, data centers and other kinds of facilities needed their backup power immediately. When the storm didn’t knock out the power, though, the facility had simply burnt fuel to generate unnecessary electricity and emissions.

Now, with technologies like battery banks and flywheels, these facilities can afford to leave generators off until they’re absolutely necessary. When the grid shuts, the bridge source will keep the energy flowing until the generator can take over.

This magazine has previously published advice on how a facility can implement new procedures to reduce its power draw (“The Lifeblood of the Operation,” Business Energy September/October 2013), but businesses can also reduce their power usage and emissions by addressing their “power factor.”

A site’s power factor is the ratio of how much electricity the facility is actually using divided by how much it is drawing from the grid. In an ideal scenario, this is a one-to-one comparison. However, motors, computer power supplies, transformer-based lighting and other equipment draw electricity in a jagged and uneven fashion, which reduces the efficiency at which it is used. According to research presented by Xzeres, some compact fluorescent bulbs, for example, have a power factor as low as 0.54. That means that 46% of the electricity the lights demand from the line goes unused-nearly doubling the lights’ effective energy cost.

To reduce this waste, companies including Xzeres, Eaton, and Leading Edge Design Group have introduced capacitor-based power factor correction equipment. This equipment captures energy when a motor’s draw cycles off and then delivers it back into the system when the motor cycles back on. In effect, this process smoothes the flow of the equipment’s power draw.

In a small-scale demonstration, Jay Boucher of Leading Edge Design Group connected one of these capacitor units in parallel with a small motor. As a result, the motor’s draw on the nearby wall socket fell from 120 W to 110 W-a decrease of roughly 8.3%. It also took 60% of wasted current off of the simulated distribution system.

In promotional material, Xzeres says that this approach can reduce a facility’s utility bill by roughly 4% each month, and the installation can pay for itself in as little as 24 months. Those reductions in cost and energy usage also reduce the company’s carbon footprint.

Warm Energy
While facilities need electricity to power lights and other equipment, this often only presents part of a facility’s energy consumption. Business may also have thermal needs-whether these be to heat worker areas or to process products. Nagle with Dresser-Rand says that many facilities are reducing their emissions by combining their onsite heat and power equipment.

Generating onsite electricity usually requires combustion, which creates waste heat as a byproduct. By reusing that heat, such as to boil water for a facility’s steam heat system, facilities managers can sharply increase their building’s overall efficiency. In one example outlined by EPA, a facility that switched to combined heat and power increased its overall efficiency from 51% to 75% and reduced its annual emissions from 45 kilotons to 23 kilotons.

Wrap Up
Ultimately, the best way for a company to reduce its emissions is to take a multi-pronged approach. Clearly, companies can’t upgrade their generation equipment on a schedule that doesn’t make financial sense, but they can choose to buy the least-polluting equipment available when it’s time to replace old machinery. In cases where financial or environmental conditions enable it, companies can install wind, solar or other renewables. If a company is limited to or chooses onsite generation that includes combustion, they can sharply reduce their emissions by tying their power and heat systems together. When it’s appropriate or cost-prohibitive for a company to build or use an onsite generator, the company can still clean it’s overall emissions profile by paying extra for renewable energy from their electricity supplier.

However, for companies serious about reducing their emissions, their best bet is to reduce their energy use. Programming lights or equipment to shut off when it’s not needed goes a long way to reducing a company’s carbon footprint-whether its emissions are generated onsite or out on the electrical grid. Making that electricity use more efficient, such as through parallel capacitor equipment, can also help.
About the Author

Matt M. Casey

Journalist Matt M. Casey writes about science and technology.

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