Ze-gen Ramps Up its Waste Gasification Process: Lessons from a Clean-Energy Startup

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Flagship Ventures, VantagePoint Venture Partners, the Massachusetts Technology Development Corporation, and an Oman-based industrial conglomerate called Omzest Group.

Ze-gen’s overall story is an illuminating one, not just for other clean energy startups, but for technology startups in general, many of which run into the same general types of problems that Davis has had to tackle over the past two years. Here’s my take on a few of the lessons:

“Invention” is not a discrete event—it’s a process that stretches out over years, and often involves sharp turns.

When I visited Ze-gen in 2007, the centerpiece of the demonstration plant was the company’s prototype gasification furnace, which would later be half-filled with molten iron. Under the company’s original design, waste was fed into the middle of the iron bath through a tube that was partially submerged in the liquid metal. This tube also supported a rotating coil that constantly stirred the iron to speed gasification.

In the combustor, the syngas is burned off; in a production system, the combustor would be replaced by a boiler or turbine to provide heat or electricity.

In the combustor, the syngas is burned off; in a production system, the combustor would be replaced by a boiler or turbine to provide heat or electricity.

The company quickly found that this system didn’t work. The torque on the feed tube from the stirring, along with the drastic thermal gradient between the bottom of the feed tube and the top, inevitably caused it to weaken and break off after a few minutes or hours of operation. (During my tour this week I got a look at an old photo of the remnants of one feed tube, floating atop the molten iron as partially melted slag.) After each failure, the tube would have to be replaced, causing great expense and delay.

“Our first feed tube cost $12,000 and lasted about 12 minutes, and four months later they cost $700 and lasted 7 hours, so there was progress made,” Davis recounts. “But ultimately we decided that having a feed tube was not the way to go. We needed to get the feedstock into the gasifier without the use of feed tubes.”

The "baghouse" removes dust and pollutants from the combustor exhaust before it's vented.

The "baghouse" removes dust and pollutants from the combustor exhaust before it's vented.

That led to what Davis calls “a major engineering modification”—essentially, a complete redesign of the the furnace. In the new design, the tube that brings feedstock into the furnace has no stirring function; in fact, it ends just above the surface of the copper bath, meaning it acts mainly as a shroud, carrying the feedstock to the zone of highest temperature before it gasifies. Also, Ze-gen switched from molten iron to molten copper, which has a lower melting point, and therefore doesn’t congeal on the tube and the inside walls of the furnace when it splashes (a major problem with the first prototype).

All of this reengineering cost Ze-gen some time, but it wasn’t necessarily a surprise, Davis says. “When you start off, you know what you want to create, and you have an idea of how you want to get there, but we also knew there were a lot of things we would have to figure out along the way,” he says. “We were confident that we could assemble a team to do that, and that if we hit a roadblock, we’d find a workaround. That is what we have been able to do.”

Scaling things up is rarely a smooth process.

There’s little way that Ze-gen could have anticipated the problems with the original feed tube and the splashing iron bath without actually building a barn-sized prototype, filling it up with molten metal, and trying it out.

“There are some technologies where you could build a version that fits on a table, and be reasonably confident that you could replicate it at a much larger scale,” Davis says. “But when you get into stuff like this, you can’t prove the chemistry in a coffee pot. If you want to prove commercial viability, you’ve got to be meaningfully scaled to do that.”

Ze-gen’s next step—after it has collected enough data from continuous operation of the demonstration plant—will be to … Next Page »

Wade Roush is a contributing editor at Xconomy. Follow @wroush

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  • Wade,

    Great article — leads to a question:
    Does the energy expended to keep the copper at 2,400-2,700 F, plus the energy required to feed and operate the gassifier, end up being larger than the synfuel energy produced?

  • Pingback: Xconomy's Roush on Ze-gen | Rethink.()

  • Wade Roush

    Good question, Bill. The short answer is no — the synfuel contains much more energy than is required to keep the gasifier up to temperature. In a commercial plant (the way Bill Davis explained it to me) part of the synfuel generated, about 30 percent, would be cycled back into running the furnace. But the way I understand it, once the furnace is hot, a large part of the energy that keeps the metal in its molten state is actually generated by the gasification process itself, which is exothermic.

  • Hi Bill,

    That is a great question! Ze-gen’s liquid metal gasification system processes carbon-rich waste material, like wood waste, and converts those materials to usable renewable fuel in the form of synags. When applied at commercial scale, the process is exothermic, meaning that the chemical conversion process will produce more total energy than is required to operate the facility, enough to keep the bath at optimal operating temperature as well as to produce syngas to make steam and/or electricity. Currently, Ze-gen is operating its pilot-scale test facility that is designed to test efficiency and operability. At this sub-optimal scale, the pilot plant does require incremental natural gas to keep the gasifier’s liquid metal bath at optimal temperature, using more input energy than the plant outputs, however at full scale, this will not be the case.

  • Tom

    Clearly this is the same technology that MMT worked on for many person-years in Fall River. That is a matter of record that cannot be disputed (c.f. USDOE technical reports – and others). The issue there, as noted, is expiration of patents – some have expired, some have not.

    I don’t think MMT/QC would go away quickly – so it is reasonable to surmise that the Sept. 18th settlement and the pending “new partner” announcement are closely related.

  • ghali hasan

    good job/ would like more info on cost a for new a unit thank’s

  • John

    What about a toxic release that injured several NB workers at the landfill. Was this related? Is the state investigating, or are they killing it because of Ian Bowles past ties to Zegen?

  • Hi John,
    The toxic release was not related to Ze-gen’s pilot facility. It occurred at the facility next door.

  • rob

    Hi, would this the process and the plant support the burning of tyres and copper,chrome,arsenic coated organic material ,if so what additional emmissions and impact do you foresee this employing on the environment?

  • Hi Rob,

    We are currently testing materials now in New Bedford. The emissions will vary by material, but we expect to put in full-scale emissions control on the commercial facility. The commercial facility will comply with any and all federal, state and local regulations regarding air emissions. You can check out more information about our plant by watching our video: http://ze-gen.com/rethink/transforming-the-way-we-view-waste

  • Ani

    would this work in municipal waste with high moisture content and low calorific value,where things like paper plastic etc have already been picked buy rag pickers ,what is the minimum BTU required ?

  • Hi Ani,

    An ideal feedstock for Ze-gen’s technology contains a relatively low moisture content and high caloric value, which is generally higher than municipal solid waste. However, we expect to blend feedstock materials that range in moisture content and BTU value, in order balance these materials with feedstocks that have more ideal moisture and energy contents.

  • Roy

    What happens to the small amounts of toxic chemicals extracted, such as arsenic? Is it captured and disposed of separately, or diluted in the syngas?

  • Tom

    The issues and questions raised by Ani and now Roy are not new, they have been addressed in the earlier MMT work, including patents and government research reports (public stuff). Maybe Cara(?) can provide these for reference, now with the settlement final as reported.

  • Hi Roy,

    Thanks for your question. The toxic chemicals are captured in the plant’s emissions control system (including a baghouse). The contents of the baghouse are periodically hauled off site by a licensed contractor.

  • rob

    hi Cara

    thank you fror your reply,could you please forward your contact details as i would like to discuss ze-gens plant and application capabilities.

  • Roy

    Thanks for your replies, Tom and Cara. I would be interested in reading some of the MMT research reports and public documents. If either of you could point me to the references, I’d appreciate it. Cara, I’d like your contact info as well. Thanks, Roy.

  • Hi Rob and Roy,
    Please feel free to contact me at cgiudice(at) ze-gen(dot)com

  • shaik

    hai Cara.. can u give me more info ….i like to develop your technology in my country,can we use wood waste only? also the cost ?

  • Cara

    Hi Shaik,

    Please visit our website: http://www.ze-gen.com for more information. Also, feel free to email me at cgiudice (at) ze-gen (dot) com.