Fuel Efficiency and Engine Options

Photo: Caterpillar

Is your genset making the most efficient use of fuel as it creates power? There’s much to consider, and it’s more than just a choice of diesel or natural gas. How about biodiesel, or gas from landfills, steel mills, coal mines, anaerobic digesters, or waste to syngas? And how about the impact of your location? Is it high altitude or high temperature? Low noise or low emission? Yes, there’s a lot to consider, and we’ve got plenty of expertise on the subject, plus a look at an amazing technology that could rewrite the rulebook on fuel usage and efficiency.It’s difficult to mention power generation without sparking a conversation about the lowest natural gas prices in years, but that doesn’t mean it’s time to say goodbye to the good old standby-diesel, and of course, that’s especially true if you’re talking about standby emergency power. In fact, Pike Research is predicting that diesel generator sets will reach 82 GW in annual capacity installation by 2018. Much of that growth reflects a need from less-industrialized countries without natural gas infrastructure, according to Edmund Campion, director of Research and Development, APR Energy, Jacksonville, FL, a global provider of fast-track, scalable power solutions.

“Natural gas is great for these long-term infrastructure projects where you have time to plan and get the pipelines done, but when you’re looking for emergency power usually the gas lines aren’t there,” says Campion.

Case in point would be Botswana, South Africa, where demand growth and supply constraints overwhelmed the Southern African Power Pool (SAPP), a cooperation of the national electricity companies in Southern Africa.

The problem was urgent, so APR Energy mobilized 70 MW of diesel power modules to a remote region outside Francistown and built a full turnkey diesel power plant, plus the staff to operate it on a 24/7 basis. Shifting from South Africa to South America, Argentina was facing severe under capacity in its supply of electricity and needed 90 MW of additional power generation resources distributed throughout the country. With many transmission weak spots in remote locations, diesel delivered by trucks was the only workable solution. But it wasn’t without some unique challenges in both the quality and quantity of fuel.

“Depending on where you are, you’d be surprised at what you find in the fuel,” says Campion. “You have challenges where fuel is a black market commodity in developing worlds, and you’re talking about a product that moves the economy, because they are depending on diesel for automotive and transportation beyond just power generation.”

He continues, “A fuel truck may leave the depot with 100% diesel on board, but there’s no guarantee it’ll come to us with that level of quality. We’ve had machinery cutting oil, or water, and other liquids contaminating the fuel. When you have a developing country that’s more industrialized, you’ll have more industrial waste. When you’re in a country that’s not as sophisticated, you’ll get more water which is relatively easy to deal with, but it’s still a problem.”

Machinery cutting oil and other things best described as … “liquids”? Now that could do some serious damage to the engine, and even if a small amount of those contaminants managed to sneak through, fuel efficiency would suffer. Is there a reliable solution?

“We do an analysis to determine the energy content with spectrometry to make sure it’s diesel rather than a hybrid with kerosene and engine oils or machine oil,” explains Campion. “And we use multistage filtration systems, so as the fuel comes off

the trucks we put it through filtration systems and centrifuges that can knock out as much of the contaminants in the fuel as possible.”

Another round of filtration takes place as the fuel is drawn into the engine, and Campion uses commercial off-shelf filtration and separation units to extend the life of the factory-supplied engine filters and boost uninterrupted runtime. For example, on a 2-MW engine, he would specify three assemblies, so two would be online at any one time, while a third one stays ready. If fuel pressures drop, the third is brought online, and the first and second can be replaced without stopping the engine.

“We can push our engine filters and extend their life by a factor of three to four times by using them as primary filtration on the engine and leaving the engine manufacturer’s filters as the ultimate protection on the engine,” says Campion. “The engine manufacturers design their filters to protect their high-pressure fuel pumps and injectors, and we try and remove as much contaminants prior to the fuel getting to those filters as possible. We can see pre-and post-fuel pressures on their filters, so we will change their filters when needed rather than by runtime hours. I call it condition-based maintenance rather than going purely by the hourly suggestion.”

Fuel filtering and treatment have a significant impact, but another factor in efficiency and equipment costs is emissions treatment. Cleaner engine emissions results in burn more fuel, and the cost is a serious issue in some countries.

“In developing countries, they aren’t sensitive to emissions, because they can’t afford it,” says Campion. “They need cheap energy to drive their economies. Industrialized nations are concerned about emissions of NOx [nitrous oxide] and CO2 [carbon dioxide], but other parts of the world don’t care. Using the latest diesel engine technology on the market does help us benefit from both better fuel efficiency and lower emissions.”

Biodiesel may well solve some of those emission problems and add to the economies of developing countries. Assuming, of course, that the fuel arrives uncontaminated, it could have less sulfur, one of the most corrosive elements in both diesel and many methane fuels, such as landfill gas. According to Pike Research, worldwide biofuels production will grow from 33.6 billion gallons per year in 2013 to 61.6 in 2023. Major oil companies, such BP and Shell, are touting their biofuel products, and in the case of BP, the company is offering refinery processing times of 12 hours.

The wide range of fuel options has resulted in many opportunities for innovative onsite power generation for GE’s line of Jenbacher gas engines.

“In about any given year, about 50 to 60% of the engines we ship aren’t just natural gas,” says Scott Nolen, product line management leader, GE Gas Engines for Power Generation, Schnectectady, NY. “They burn natural gas, syngas, coal mine gas, fuel gas, which is from oil fields. The fuel gas may have a bit of natural gas, but it’s much less treated than typical natural gas. Then, we have projects with landfill gas, and one of the more interesting new developments we see are steel gas applications, with a number of nice projects coming out of South Africa and China, plus a few more from different places around the world.”

According to Martin Schneider-also a product line manager, GE Gas Engines for Power Generation-gas from the steel plants worldwide could deliver 30 to 40 GW of electricity.

Jenbacher also developed special technology to successfully burn syngas in its engines.

“With syngas, the challenge is not really the heating potential, because it is quite good at about 130 BTU,” says Schneider. “The challenge is with a waste as a feedstock which is never homogeneous, and the gas has NOx, so you have very stringent emission requirements, which are very challenging.”

The syngas technology will see global applications under a recently announced an agreement with GE and Green Waste Energy (GWE), Greenwich, CT. The plan calls for Jenbacher gas engines at a series of Advanced Recycling and Energy Conversion (AREC) plants that GWE’s development subsidiary, Green Waste Energy Development (GWED), plans to build around the world. The Jenbacher J620 gas engines will use the syngas produced at GWED’s waste-gasification facilities to generate renewable electricity. Each installed gas engine will generate nearly 2 MW of onsite power. But the power production can rise. For example, a waste-to-energy power facility at Pebble Hall in Theddingworth, UK, will use up to six Jenbacher J620 gas engines for approximately 8 MW per hour for use on the electrical grid.

“This is a great opportunity for syngas projects,” says Nolen. “The initial project uses wood mass for the gasification process, and we have a number of engines running under those circumstances, and also using municipal solid waste.”

No matter the process to extract it, gas from biomass or municipal solid waste requires a genset manufacturer to do their homework at the factory, but that’s often just the beginning of the job, according to Justin O’Flynn, general manager for Europe, Middle East, and Russia, Cummins Power Generation, Minneapolis, MN.

“When our commissioning engineers get onsite, they validate the factory calibration and, if necessary, adjust it,” says O’Flynn. “We are seeing more biogas or producer gases coming from landfills, digesters, and sewage. If you compare the energy content to natural gas in terms of BTU per cubic foot, natural gas has about 1,000 BTU per cubic foot versus 450 BTU per cubic foot for biogas, and then if you go to synthetic or producer gases, it comes down to only 150 BTU per cubic foot. The challenge for the technology is to make a gaseous-fueled engine that can run on these fuels with vastly different energy content.”

Running gensets with “lean-burn” technology is part of the strategy.

“Lean-burn means there is an excess of air needed for combustion of the fuel,” explains O’Flynn. “It’s typically about 9% by volume of excess oxygen in the exhaust gas. So, as the energy content of the gas is reduced by a factor of 50%, you can see that the volume of gas that has to get into the engine has to increase accordingly. The engine management systems are continually sensing the atmospheric conditions that can affect the lean-burn operation of the engine. They measure temperature, pressure, and humidity, and algorithms used by the engine ignition control systems predict the future conditions of the air to ensure optimum performance.”

Cummins’ QSV91 lean-burn gas engines and Cummins Generator Technologies’ STAMFORD alternators were specified for a biogas-fueled CHP project at the Riverside Sewage Treatment Works in London, UK. Broadcrown Ltd, UK, an independent manufacturer of power generators and generation systems, cited Cummins’ fully automatic electronic management and sophisticated engine-monitoring systems as critical factors in the project’s success. Plus, the generator sets also delivered high fuel efficiency, and low NOx exhaust emissions.

Methane gas from anaerobic digesters, landfills, and even coal mines requires constant monitoring and special attention to engine design, notes Harlan W. Martin, president, Martin Machinery, Latham, MO.

“You have to pay attention to the bearings and avoid yellow metals,” says Martin.

Martin Machinery’s engines also use special air-fuel ratio controls to monitor the oxygen content in the exhaust. As the fuel BTU content varies, the controls compensate by changing the air-to-fuel ratio automatically.

“If you have a large dairy farm with an ice cream or cheese plant close by that can supply some byproduct, it can boost the BTU gas ratio,” explains Martin. “So we use the air fuel ratio controller to keep the engine at the optimum efficiency.”

For diesel-fueled engines in standby emergency power applications, the BTU content doesn’t have as much variability, but the fuel is susceptible to other problems, and Martin has advice for proper storage management.

“In a standby diesel with industrial commercial facilities, you need an adequate supply to run 48 hours at a minimum,” he says. “Even with the typical testing done in a year’s time, the fuel can get stale and have algae and other problems.

“There are additives that can be used to prevent that, and on farms we recommend that they use the same diesel supply from the generator for the farm equipment, such as tractors and combines,” he continues. “Just make sure that the tank doesn’t get below one third before refueling.”

Refueling isn’t an issue with natural gas from a gas utility. And it’s proven to be reliable, as evidenced by the distributed energy projects that kept running during Hurricane Sandy’s visit to the East Coast. For example, a co-op tower in Greenwich Village maintained full electricity and heat, supplied by a CHP system from Tecogen, Waltham, MA. Four of the company’s InVerde units run 24/7 at the co-op, and because it relies on inverter-based technology, it’s a microgrid that can function during a utility failure.

That’s important for maximizing your runtimes, according to Robert Panora, president and COO, Tecogen.

“In New York, Con Edison doesn’t like to see synchronous generators on their circuits, so you can’t make power during a blackout unless you have an inverter interface,” says Panora. “An inverter-based machine has something called anti-islanding, and if there’s an outage we could shut off the connection in the engine and continue running the CHP plant.”

Whether the fuel is diesel or some form of gas, maximizing your runtime is a critical factor in maintaining efficiency, according to Nick Kelsch, gas application consultant at Caterpillar Inc., Electric Power Division, Mossville, IL.

“Most of our customers in a biogas environment have a goal of operating at full power 24/7,” says Kelsch. “And when you’re running the engine you’re making money, but planned maintenance has to be considered, because if you want to run 24/7 you can’t do it forever. If your maintenance plan dictates that you can only run 8,000 hours instead of 8,700 hours a year, you can have the most electrically efficient engine in the world, and it won’t outdo an engine that can run 8,500 hours per year.”

High runtimes played a key role in a project in Ontario, Canada, where the City of Markham recently purchased a CG260-12 Cat generator set for the MDE Birchmount Energy Centre, and a CG260-16 generator set for the Bur Oak Energy Centre. The CG260 generator sets provide a combined heat and power solution for 7 MW of electricity and 7 MW of thermal energy to the Markham’s district energy systems. These projects will be the first in North America to employ Caterpillar’s recently introduced CG260 Series of high-efficiency gas generator sets.

According to Pike Research, installations of natural gas gensets from 2013 to 2018 will total 60 GW of capacity and produce almost $10 billion in annual revenue, by 2018.

“Folks in the utility business value equipment reliability and durability above all else,” says Kelsch. “With bigger engines, the RPMs tend to spin slower, and you get reliability and durability, and longer maintenance intervals. So, at the end of the day, you see lower total operating costs.”

A major overhaul for the GG260 is scheduled at 80,000 operating hours. That’s significant when compared to higher speed engines that typically require major overhauls around 60,000 to 65,500 hours. The CG product line also boasts 4,000-hour intervals between spark plug maintenance. Oil changes and plug replacement are designed to occur simultaneously to reduce downtime.

In an additional nod to the potential for CHP applications such as Markham’s, CG products include Cat’s Total Electronic Management (TEM) control system. It’s designed to optimize genset performance and can control an entire power plant from a single, common touchscreen interface.

According to Kelsch, sophisticated technology has also evolved for many of the ancillary devices on gensets.

“Twenty years ago, all of our gas engine generator sets provided a lot of mechanically driven devices such as pumps,” says Kelsch. “But now, electrical pumps are driving heat circuits, rather than mechanically driven systems that reduce efficiency. It lets us do heat recovery more efficiently, by providing heat exchanges rather than radiator-cooled systems to capture the heat energy and better controls for monitoring and controlling. We’re now working with our dealers designing and selling heat recovery systems that are mounted on a skid. So it’s self-contained and co-located next to the generator set.”

Another technology that has improved efficiency applies the self-contained philosophy to the fans and radiators that cool engines, according to Rick Dezek, sales manager, US, Sutton Stromart Ltd., Racine, WI.

“We’re talking about remote radiators for continuous duty applications,” says Dezek. “So, instead of radiator fans that are driven off the engine, we use electric motors.”

The electric fan motors reduce the parasitic load normally found on mechanically driven systems, and Dezek notes that the impact to efficiency is significant.

“Mechanically driven fans on those big engines often draw over 100 horsepower,” he says. “However, these remote systems use multiple small-diameter fans that are typically 10 to 15 horsepower apiece. So now a radiator could have three fans with 15 horsepower each, for a total of 45 horsepower. That’s a drop of half the parasitic load and adds about 50 kilowatts electrical capacity. That can be worth something to the customer, and it’s important in the developing market for natural gas power plants.”

Another benefit is reduced noise. Dezek says Sutton Stromart systems register about 80 dB, rather than the 100 dB levels typically found on standard systems. Even less noise is possible if the fans use a step-start strategy. Depending on the ambient temperature, it may take just one fan to cool the radiator. Variable frequency controlled fans are another option, and they can run at lower sound levels as they turn slower.

“We have sold radiators with 14 fans,” recalls Dezek. “The design was a tabletop style radiator, 18 feet long and about seven feet wide, with 14 fans. All motors were wired into a starter panel that can step-start one at a time. Often, the strongest requirement for low noise is at night, and lower night temperatures allow us to run fewer fans.”

We began our examination of fuel and engine options with categories of diesel, biodiesel, gas from landfills, steel mills, coal mines, anaerobic digesters, and waste to syngas. However, there’s a new engine design on the horizon, and it’s capable of record breaking thermal efficiency by combining two fuel sources. It’s known as Reactivity Controlled Compression Ignition (RCCI). The RCCI approach applies a dual-fuel engine combustion technology. It’s an ongoing program that was developed at the University of Wisconsin-Madison Engine Research Center laboratories and has the potential to dramatically lower fuel use and emissions.

“This is a very high-efficiency, low-emissions technology for reciprocating internal combustion engines,” explains Dr. Rolf Reitz, Wisconsin Distinguished Professor of Mechanical Engineering at the University of Wisconsin-Madison.

Reitz is also director of the Engine Research Center (ERC), and current director of the ERC’s Direct-injection Engine Research Consortium. The consortium boasts a membership representing all the major engine manufacturers and related organizations such as the Department of Energy.

“The idea is that you run a reciprocating engine in a compression ignition mode, such as a diesel engine,” says Reitz. “But the difference is that, instead of injecting the fuel close to center when the pressure is the highest, it’s injected much earlier, and that allows time for the fuel to mix with the air.”

The RCCI approach could eliminate the high cost of emission treatments such as selective catalytic removal (SCR). “We are suggesting that instead of using after treatment like urea, we use two fuels in the combustion chamber,” says Reitz. “So, it can work with gasoline and diesel fuel, or natural gas and biodiesel. Any two fuels that have differences in reactivity can be used.”

Efficiency is equally impressive. Reitz has demonstrated 60% thermal efficiency from an RCCI engine.

“The combined cycle gas turbine power plants you hear about in the hundreds of megawatts can get 60%,” explains Reitz, “but the only reason that is, is because they’ve invested millions of dollars in a huge-scale facility. The bigger the engine, the less surface-to-volume ratio, so there’s less heat loss. If we wanted to make our engines as big as a 500-megawatt powerplant, we would have even more efficiency.”

Higher efficiency, plus fuel flexibility and low-cost emissions, all in one package? Yes, it sounds too good to be true. Nonetheless, RCCI technology is moving forward fast, and Reitz says the engine manufacturing industry is excited about the results. All told, the progress from traditional technologies, plus breakthroughs such as RCCI, make for a positive outlook in fuel and engine development.

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