May-June 2009

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Turbines Running on ... Renewables

Never mind wind power: Hydrogen from biomass is becoming viable for off-grid power.

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By David Engle

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The system which IR mated to its microturbine is one patented by Solenia SA of Camorino, Switzerland; Solenia is the pyrolysis subsidiary of CO-VER Energy Holding, which support virtually the full spectrum of renewable technologies and alternative fuels.

As noted earlier, the small pilot plant is now powering IR’s first application, in northern Italy. Although, at present, only one turbine is being fueled with the pyrolysis yield, Watts points out that the plant is scalable, and it could easily run multiple generators.

How about the tiny plant’s commercial prospects as an energy generator?

Watts mentions that, in Europe, favorable feed-in tariffs strongly support renewables and, thereby, assure an eventual return on investment.

Solenia’s sales manager Stefano Bianchi also provides the following operational specifics:

With the pyrolysis chamber working virtually round-the-clock (as designed) or for an average of 7,500 hours per year (i.e., 20-plus hours per day), and stocked with wooden chips at 40% relative humidity at the dryer inlet, this volume of feedstock would enable production of “about one megawatt electricity,” using four of IR’s 250-kW turbines.

“The gas produced by our pyrolysis reactor in this case is about 720 cubic meters per hour … and is mainly composed of methane, hydrogen, carbon monoxide, and carbon dioxide,” he adds.

Pyrogasification system from Swiss renewable-energy specialty firm, Solenia SA, can extract gases from a range of biomass sources.

The steady input of woody stock needed to yield this volume would come to about 2,000 kilograms per hour; or, to put it another way, “2.8 kilograms of wood makes one cubic meter of gas [i.e. 0.36 cubic meters per kilogram],” explains Bianchi. Average electrical efficiency comes to 20–25%; cogenerated heat utilization raises this to 70–80%.

The total turnkey cost: from 2,500 to 6,000 Euro per kilowatt electrical (kWe) installed, depending on plant size.

Bianchi adds that, using the other kinds of potential biomasses, “You need different quantities of material to reach the desired electricity production, as every biomass has a different heating value.”

As for running continuity: Once the temperature reaches its critical point, “the reaction is stable and the gas production is continuous—provided you properly feed the reactor.”

Reactors are equipped for remote monitoring and control. And, when evaluating a site for possible development or for other testing purposes, a mobile portable pyrogasifier, capable of yielding 50-kilogram-per-hour biomass may be sited initially, prior to installing a pre-assembled modularized plants (250–1,000 kWe) for automated, continuous operation. Output of electricity and heat is currently available in the 500-kW–10-MW range.

Burners, Adapting to Change
Running turbines on “boutique” fuels poses a few technical challenges to ignition systems, which, either slightly or significantly, must be reengineered.

Hydrogen, for one (again, that’s the gas made by both the just-described pyrolysis and goal gasification), displays radically different combustion characteristics from methane: specifically, notes Acharya, “higher flame speeds … and a tendency for flashback,” when put through the standard premix injectors that are designed for natural gas. “You can’t just replace natural gas with hydrogen,” he says, as the flash will destroy the burner. Next Page >

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Turbine,
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May-June 2009

Turbines Running on ... Renewables

Never mind wind power: Hydrogen from biomass is becoming viable for off-grid power.

By David Engle

Turbines whirring … churning … roaring: pushed by wind, steam, water, or fuel. They’re the workhorses of global electrification. One way or another, turbines make almost all the electrical power on Earth. In the transition from a hydrocarbon-fueled economy to a next generation suite of renewables, the ever-spinning rotors have established themselves as a fitting constant, spanning both energy eras.

Natural gas, as a fuel for turbines or any power generation, is still hard to argue against, but changes are in the wind. Although not renewable, of course, new natural gas reservoirs still seem to pop up here and there, and the nation’s pipeline makes distribution of methane or liquefied gas very easy. As for its efficiency, gas, of course, can make both combined heat and electricity (or, at a central power plant, enables impressive combined-cycles efficiency).

Regarding emissions, when best-available technology is used, the results are considered quite acceptable, if not perfect. Nevertheless, with each passing year, the inherent drawbacks of gas make it a bit less appealing, especially in comparative terms with the fair-haired darlings, green and renewable. Also, for some time now, natural gas has been facing ever-tougher nitrogen oxide (NOx) restrictions in southern California, East Texas, and other choice power markets. Per-MMBtu (one thousand, thousand British Thermal Units) rates have crept up for a decade-plus—in some areas, spiking frighteningly.

Vulnerabilities remain, too, for securing reservoir supplies that are remote and must be protected by US forces, bought with dwindling dollars, and transported a long way home. Gas market volatility and manipulability are chronic issues. And, increasingly, tariff and policy incentives favor renewable alternatives—steering fueling choices even further that way.

One way or another, the luster of natural gas for power generation, though far from gone, is rapidly fading.

Refueling, Retooling, for Syngas and IGCC
Thus, beginning a dozen-plus years ago and gaining steam in a hurry of late, there’s been almost a global mania for eliminating dependency on fossil fuels, especially ones coming from not-always-friendly petro states and, better still, developing one’s own domestic renewables.

Also on the wish list of desired fuel traits are these two: Next-generation prime movers must remain affordable and their bad emissions minimal. We’re talking, of course, about both gaseous and liquid fuels for power generation, and maybe new liquid ones for transportation: ethanol, butanol, and biodiesel (then again, maybe not—given reported advances in all-electric cars).

In any case, quests for new fuels for vehicles and power generators are both underway. In some ways, they’re independent challenges; in others, interrelated. To run turbines with something other than natural gas, several tracks are in progress, notes Sumanta Acharya, a professor of mechanical engineering who heads a turbine research center at Louisiana State University (LSU), in Baton
Rouge, LA.

In the “lead” for years, alternative fuel-wise, he says, has been the push to develop coal-derived syngas. Under the Bush administration this was prioritized as our national energy policy. In the past decade, hundreds of millions of Research and Development dollars were spent on a concept that produces hydrogen (H2) rather cleanly from coal, then burns the gas cleanly, again, to make power.

As he explains, coal is first super-heated at high pressure, without much oxygen; the resulting gases that are emitted—after they’re cooled and cleaned—are ready for burning. Heat input to this “integrated gasification combined-cycle” (IGCC) process makes both the gas fuel and cogenerated electricity. Useful byproducts include ammonia, methanol, sulfur, and some others. The ultimate vision here is to supplement natural gas with an alternative one, and perhaps even someday replace it.

As for the present status of this ambitious undertaking, at this writing the US Department of Energy (DOE) is pushing, Acharya says, to build a prototype “zero-emissions demo plant.” If IGCC technology proves itself on cost and quality values, we might then see a proliferation of zero-emission, hydrogen-fueled power plants. They would become the backbone of America’s next-generation energy solution. And as their prime feedstock, they’d rely on the continent’s enormous coal reserves.

Though not renewable, of course, that supply is deemed sufficient “for about three centuries of projected demand,” says Acharya, citing commonly acknowledged figures.

Besides taking coal as a raw material, the IGCC process can also accept heavy oils, petroleum coke, biomass, and waste fuels—and render them all cleanly into gas. Assuming—correctly, in Acharya’s view—that the cost of gasification can be brought down enough to be competitive, H2 will emerge as the clean, abundant, cheap, and entirely domestically generated next mainstay fuel.

“Over the last few years, these things have started to look quite cost-competitive, particularly when natural gas prices were high,” he says.

On the negative side, though, coal mining remains nasty, dangerous work, and environmentally disruptive. So, despite synfuels’ comparative virtues, they’re perhaps not the perfect ideal yet. Although synfuels have lost just a tad of the allure they enjoyed initially, they remain—at least until the Obama administration makes a change—a central DOE fuel objective, Acharya notes. And, important research and innovations aimed at reducing the production cost are still ongoing, globally.

Microturbines Fueled Onsite … By Pyrolysis
Hydrogen derived from this coal process would be aimed primarily at running centralized electric plants; but what about alternative turbine fuels specifically for distributed power? Here, another similar gasifying process, called pyrolysis, has lately been introduced near the Alpine region of northern Italy to power an Ingersoll Rand (IR) microturbine in an onsite, renewable power role, IR reports.

Pyrolysis—more apt for woody waste, which is abundant in many parts of the world and easier to get at than coal—promises potentially far-reaching usability. Though not as widely known as ethanol or methane digester gas, notes IR business development and marketing manager, James Watts, wood pyrolysis gas “is something of an alternative to biomass” as a fuel. An onsite pyrolysis plant offers the appeal of renewable distributed energy—without being tethered to a landfill or wastewater treatment plant for its renewable fuel.

“The beauty of pyrolysis, [compared with digestion reactors], is that you can use more lignin-based materials [like] corn husks or rice,” continues Watts. “It’s not digestion”—as is the case with the organics yielding gases in any bioreactor.

“You’re not just limited to carbohydrates and fats [and digestible organics] … of that nature,” again, typical of many municipal waste streams,” he adds. “You can use more cellulosic types of sources,” such as are found at granaries, farms, poultry coups, in forestry, at lumber mills, and at scrap wood or other plant vegetation sites.

These woody sources are typically less amenable to anaerobic digestion at a treatment plant relying on microbes, which also need controlled conditions.

By contrast, the material for pyrolysis can be gathered, dried in the air or sun as needed, and simply fed into a pyrolizer for rapid rendering into gaseous fuel.

To begin the process, heat is first applied in the absence of oxygen or other reagent; soon, gases are emitted, effectively “kick-starting” its own pyrolyzing fuel source, so that the cycle becomes both self-sustaining and a net fuel and energy gainer.

At the end of the sequence, gases emerge for collection “as a nice mix, that we’ve been able to get to work successfully with our microturbines,” name-plated at 250 kW, says Watts.

Besides the woody materials noted above, other potential feed stocks might include dedicated produce like palm oil, rapeseed, or sunflower oil, for example, or mixed animal and vegetable biomasses, green cuts, straw, vegetable waste, and livestock manure, even having high-moisture content, according to product literature from a pyrolysis firm.

For preparatory drying, exhaust heat from the engine can be applied.

Pyrolysis process speeds can also be hastened, and raw ingredients varied, to suit whatever stock is available and to alter the gaseous proportional outcomes—H2, carbon monoxide (CO), carbon dioxide, methane, and others—as desired.

Gaseous outputs are then dried and prepared to run engines. Even the ash can be recycled into high-quality fertilizer.