Archive for January, 2011

Harmon P68 fired with Grass at the Ashoken Center

There have been several requests for me to explain our experiences burning grass pellets in the appliances being used the Catskill Grass Bio-Energy project.

(Please note:  any mention of brand names is for informational purposes only, and is not intended as an endorsement of a particular product.)

Our first purchases were two Quadrafire Mt. Vernon pellet stoves. One was quickly installed and the other put in storage for later installation. We also purchased two Central Boiler Maxim pellet hydronic furnaces. One was sited at the Town of Franklin NY Town Garage where the first Quadrafire was installed in the Town meeting hall in the same building. We were able to secure the services of a local plumber who completed the installation by the end of December that first year.

Initial operation of these first units had a steep learning curve. The Maxim furnace burned well after the operator at that site tried many combinations  of feed rates and blower settings. Neither the manufacture nor the local dealer were of little help tailoring the settings to burn grass. Luckily the operator at the site had a lot of experience in the heating industry and had interest in making the unit work to its potential. As the season grew colder we found that if the unit was pushed to produce maximum heat it had a tendency to melt the aeration paddle on the end of the feed auger. The original was mild steel but the replacements were made of stainless steel. They did last longer but eventually failed as well. We kept replacements on site after the third failure. Another shortcoming of this unit is the size and position of the ash drop. Ash has to be removed by scooping the ash out daily also the unit has to be shut down weekly to clean the interior of the burn area and the heat exchanger. If this is neglected the unit pushes smoke back into the hopper on top of the furnace leaving a creosote type of condensate in the hopper. Another problem with the design of this unit caused two burn backs into the top hopper. We are not sure the reason for the first but the second was the result of a power outage lasting six hours. The unit needs a supplemental power source to run a clean-out cycle if high heat is experienced or a power outage is experienced. By the way, the unit was burning wood pellets at the time of the power outage.

As to the Quadrafire at this site, the operator tried all season to burn grass with little success. Any of the settings on the control unit did not dump the ash fast enough and the fire was snuffed out. We purchased these stoves based upon the success of Dr. Cherney at Cornell University. We knew we needed specific tables to burn grass successfully. Dr. Cherney supplied us with the tables that the manufacture had supplied. We were unable to install the grass tables. We sought help from several Quadrafire dealers and the manufacture and were told multiple times that Quadrafire does not support burning grass pellets even though we knew grass tables existed. After that initial season we pulled the unit and replaced it with a Harman P68 which has been burning well ever since. The Harman has analog controls for feed rate and also has a unique burn system where the pellets are pushed up a burn ramp and the ash is pushed off the ramp into a very ample and removable ash pan.

We have four Harman stoves on site at this time, Two P68s and two P45s. These units are working well burning grass pellets, but, like all appliances burning grass, they require frequent cleaning. Anyone wishing to burn grass with  appliances that are not specifically designed to handle grass will need the owner/operator to be conscientious about operation and cleaning.

More about the Quadrafire saga (we are using them satisfactorily)  and our other appliances and installations next time.

Keep Warm!


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I often feel like I am having trouble keeping up with the current status of grass energy research and development. Just when I think I have a grasp of the scene, I get surprised by some new revelation. This happened most recently when I downloaded the Technical Assessment of Grass Pellets as Boiler Fuel in Vermont. This 46-page report was produced by the Vermont Grass Energy Partnership, a collaborative effort among the Vermont Sustainable Jobs Fund, University of Vermont Extension Service, and the Biomass Energy Resource Center in Montpelier (BERC). Various people have critiqued this report in this blog and elsewhere and I am not planning on using this space to give it a full review. Despite its flaws, real or perceived, I applaud Vermont for supporting grass energy research and development through the Sustainable Jobs Fund and wish that New York State had a similar commitment.

The Vermont study was by its own admission limited in scope and will therefore prompt further research. Citing the report’s “Next Steps” section:

The next steps in determining the feasibility of grass energy in Vermont should include a robust economic assessment of the costs of manufacturing grass pellets under different scenarios. For instance, what changes can be anticipated at a centralized (stationary) pellet mill compared to utilizing mobile equipment (at different scales) to process the grass “on location?” As part of this economic assessment, key variables such as the cost of energy (fuel, electricity, diesel, biodiesel, etc.), subsidies paid to farmers (e.g., USDA’s Biomass Crop Assistance Program), and economies of scale in production costs must all be considered. Once the grass pellet production costs are fully understood, target wholesale and retail price points can be projected and compared against other heating fuels, including liquid fossil fuels and wood fuels.

As part of these next steps, the report also states that research will be needed to:

• Examine new and existing heating appliances (furnaces and boilers) that claim the ability to reliably burn high-ash fuels such as grass pellets.
• Determine the production costs of pellets made with grass and wood blends and to gauge the interest of the pellet consuming market for this type of product.
• Assess the production costs of farm-scale grass pelletization and the potential fuel savings of grass pellets over other heating fuels. Other market development scenarios using 100% grass pellets could emerge that will need further in-depth analysis as well.

That’s a decent grass pellet research agenda. Recently, the Vermont Sustainable Jobs Fund issued a request seeking proposals that will: “…. lead to the design, fabrication, demonstration and use of a mobile or stationary pelletizing system capable of converting at least 1-ton of grass biomass per hour into densified fuel. Projects must be able to identify at least one in-state source of grass biomass that will be pelletized and at least one in-state end-user of the pelletized fuel.”

Others, notably Renewable Energy Resources LLC and Broome Biomass LLC are researching briquetting (or cubing) densification as well as feedstock harvesting and handling methods to produce grass fuels for larger boiler/CHP applications. Still others, such as Jerry Cherney at Cornell, Michael Newtown at SUNY Canton and Paul Cerosaletti of Delaware County Cornell Cooperative Extension are examining the combustion characteristics of grass fuels in commercial and residential-sized units. Also, we should not fail to mention the mobile pelleting work of the Hudson Valley Grass Energy Group and the Pocono-Northeast RC&D Council in Pennsylvania. Last, the work of the Resource Efficient Agricultural Program (REAP) in Ontario, Canada is well known.

My intention here is not to try and provide an exhaustive listing of all the research that may be ongoing, but rather to ask the question: “Are we, the grass energy community, covering all the research and development bases in a coordinated and comprehensive way?” Yes, different people are looking at different pieces of the puzzle, but are we really working together in a truly collaborative manner? Perhaps it is time to convene a special-purpose conference for the relatively small cadre of researchers and business interests to review progress, compare notes and chart out a research and development course that will get us to the goal of a viable grass energy industry.

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The Vermont Grass Energy Partnership recently released a report titled “Technical Assessment of Grass Pellets as Boiler Fuel in Vermont”. A more fitting title would be “Yet another demonstration that grass biomass can be pelletized and combusted but is a more problematic fuel than wood”. The study does demonstrate the process, but it offers little if any new technical information, and I question why this work was even considered for Federal funding unless its proposed scope was more ambitious than what is represented in the final report. The topics covered in the report have all been addressed, and in much greater detail, by previous research. Indeed, the references cited in the report’s own bibliography, in particular the one by Jenkins, et al., contain far more useful technical information on slagging, corrosion, and emissions than this study. I have included a list of articles below. The length of the list is limited by the blog word count, not by the number of relevant references: there are dozens in addition to those listed and they can easily be found via web search. This is not to say there remains no worthwhile research to be done.

The problematic characteristics of grass fuel remain mostly unaddressed and call for work on innovative solutions. The mechanical problems related to ash fusion and clinkering have been largely dealt with already in multifuel boilers. Fuel leaching by natural or artificial means can also be employed to remove much of the low fusion temperature alkali chloride ash components. This also reduces the corrosive effects of chlorine in the flue gas. Another option is microground grass fuel burned as an explosible air entrained powder. In this case, the ash particles cool before they have a chance to agglomerate. I do not believe that the clinkering issue presents much of a technical challenge, except for residential scale pellet stoves which, for the most part, are not yet designed to have multifuel capability.

The corrosion and emissions issues posed by grass fuels are more difficult. Obviously, reducing the nitrogen, sulfur, and chlorine content of growing grass is the most straightforward approach. Grass type, soil chemistry, and fertilization practices all impact the chemical content of the growing grass and harvesting practices further impact the final chemical composition of the feedstock. I am not an agronomist and am ill informed about ongoing research in this area. I think it’s safe to say that standard best practices have yet to be established. Properly designed multifuel boilers use corrosion resistant materials and can reliably combust grass fuels. As mentioned above, chlorine content can be reduced by leaching and NOx and PM emissions can be reduced to some extent by carefully controlled staged combustion and exhaust gas recirculation. Finally, there are well established methods for flue gas scrubbing that can be employed if necessary. Cost effective small scale flue gas treatment methods need further development work.

I was surprised that the report contained no information regarding important details of grass pelleting, in particular how the process must be modified with grass and grass/wood mixtures. Were different dies used? What other process parameters were modified?

Finally, I think we should be looking at other grass fuel forms aside from pellets. Just as with woody biomass, which is typically burned as chips in non-residential boilers, baled grass is the form of choice for lowest cost local use. Efficiently stacked or containerized bales can have an effective bulk density of 15-20lb/cuft, comparable to wood chips. In my next blog, I will discuss the merits of containerized bulk biomass solutions.

PS – I apologize in advance for my negative reaction the Vermont study. My opinion is just that, and is not intended to impugn other efforts by the members of the Vermont Grass Energy Partnership.

References – available on the internet for free

Thomas Nussbaumer
Combustion and Co-combustion of Biomass: Fundamentals, Technologies, and Primary Measures for
Emission Reduction
Aerosols from Biomass Combustion

B.M. Jenkins et. al.
Combustion properties of biomass

E. Bjorkman and B. Stromberg
Release of Chlorine from Biomass at Pyrolysis and Gasification Conditions

Peter Glarborg

Hidden interactions—Trace species governing combustion and emissions

References – available on the internet for a fee

P. A. Jensen et.al.
Transformation and Release to the Gas Phase of Cl, K, and S during Combustion of Annual Biomass,
Pretreatment of straw for power production by pyrolysis and char wash,
Removal of K and Cl by leaching of straw char,
Experimental Investigation of the Transformation and Release to Gas Phase of Potassium and Chlorine during Straw Pyrolysis

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This grass blog has focused mainly on the practical aspects of stoves, boilers, and developing a market for grass combustion. The previous posts show a common acceptance of a certain beauty and simplicity integral to growing and using a fuel so appropriate to upstate rural New York, but we have not paid much attention to the underlying systems. For me, one of these dynamic subsystems is soil, a topic that takes high priority – not only because harvested biomass subtracts from the soil – but also because part of the rationale for biomass is carbon neutrality which is mediated between plant photosynthesis, soil, decay, and the atmosphere. Soil is important because, like fossil fuels, its replacement takes place over geological time. It takes 200 to 1000 years to rebuild topsoil naturally to a depth of barely one inch. And, like so many agricultural endeavors, combusting biomass is a low-profit transaction – low profit at both the point of raw material sales and of densified finished product. So – as has happened to agriculture in so many places – the temptation is always to produce on a larger scale in order to increase profit.

I am not a soil scientist and this brief summary of soil ecosystems comes from a more expanded discussion in a book called Nature’s Services edited by Gretchen Daily and published by Island Press in 1997. Some of the ecosystem services listed that soil supplies are

  1. Participation in the hydrological cycle where certain characteristics of soil (ie organic content) in combination with growing plants protect it from erosion and transpire water back into the atmosphere.
  2. Retention and delivery of nutrients to these plants. This also depends on soil organic matter, as well as species diversity both in plants and soil bacteria.
  3. Disposal of wastes and dead organic matter through decomposition, recycling and diverse microbial species closely related to 2) above
  4. Participation in the regulation of the biogeochemical cycles – particularly carbon and nitrogen, which are very interdependent, vary in different climates and seasons, and are not completely understood.

It is almost impossible to put a price on these services, but estimates are always in the billions of dollars. A new school of economics, Biophysical Economics, formed as a response to energy and environmental events of the 1970s, uses thermodynamics and the study of energy flows as additional explanation for economic systems. These economists recently had their annual meeting in, of all places, the State University of New York’s College of Environmental Science and Forestry in Syracuse (2009). Ecological Economics, another non-main-stream economic school of thought, which sees human economy as a subsystem of a complex global ecosystem, has developed from Biophysical Economics.

All this is important because standard classical economics, based only on the laws of human supply and demand, does not sufficiently explain the kind of thinking that must be the basis for biomass energy. The “profit” in biomass energy must recognize the synergistic effect on the community and the value of ecosystem services to be profitable. The real agricultural battle is not between food and fuels, but between food, fuels, and the health of the environment. Unless humans learn to do the equivalent of tithing back to the ecosystem we will overuse it. In my opinion, biomass, in order to really make sense, must be more than just a part of alternative energy but also a part of alternative economics, a revolution in what capitalism encompasses.

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