The Mariposa Biomass Project

The Mariposa Biomass Project has been exploring the idea of a woody biomass facility in Mariposa County that would use slash from forest thinning projects for the generation of bioenergy and commercial byproducts.  The facility would produce a revenue stream that should help finance forest thinning projects, attract new industries and jobs to the County, and possibly have other positive economic and environmental benefits for the county and the region .   Much of the impetus for this program is the growing recognition that we need to reduce the fuel load in our forests for the sake of forest health and fire safety.  The big question is what is the best way to deal with the slash produced in this effort with respect to costs and benefits to the environment, climate change and our local economy?

As the County considers such a program there are many factors to consider:  What is the sustainable level of the biomass supply? What is the right type and sized of woody biomass to energy facility to use? Where should it be located? How can it be financed?  Are there environmental or other groups likely to oppose this project and for what reasons?

After initial discussions, the type of facility chosen was a pyrolysis reactor facility rather that some kind of combustion facility (further explained below). As for the other questions, Mariposa Biomass Project, with help from the Sierra Nevada Conservancy and County administrative staff, has received a grant from the Statewide Woody Energy Team (SWET) for a "pre-feasibility opportunity scan" and a technical advisor is assisting our group through the process of answering these questions, plus the aiding the process of funding and facilitating the project in general.

As mentioned above, of particular interest to Mariposa Biomass Project are biomass reactors that use pyrolysis or gasification (thermal decomposition in the absence of oxygen) to produce energy, rather than one that uses combustion (burning the biomass in the presence of oxygen).   There are currently more than 100 biomass reactors in California using combustion, but none can meet current air quality standards because of particulate emissions and NOx. Furthermore if rated in terms of carbon dioxide, CO2, produced per kWh of electricity, burning biomass to produce electricity does not compare well with competing power plants, is therefore considered "dirty" and not clean green energy.

Gasification (pyrolysis) facilities can be operated in such a way as to convert the hydrogen in the biomass into syngas (a synthetic gas composed largely of hydrogen gas and some carbon monoxide), which can be cleaned up, then be burned in a generator to produce electricity while meeting air quality standards. At the same time, much of the carbon in the biomass is converted to biochar.  Biochar is a fine-grained charcoal like substance, essentially pure carbon, which can be sold as a soil amendment and other products.  When biochar is used as a soil amendment, it improves soil fertility, the soil's ability to hold water and nutrients, and agricultural productivity in general. It also effectively sequesters much of the carbon from the biomass in the ground for hundreds if not thousands of years. Thus a biomass reactor optimized for biochar production has significant advantages in terms of the environment and climate change over the older style biomass reactors that simply burn biomass to generate electricity, but in the process quickly release significant amounts of greenhouse gasses into the atmosphere.  (See Footnotes 1 and 2 below.)

A ½ MW biomass/biochar facility designed and operated by Phoenix Energy has been in operation in Merced for several years now and they are selling their biochar for $2 a pound to gardeners and for $0.79 a pound in truckload quantities, thus enhancing their revenue stream over just producing electricity. The Merced facility receives 40% or their revenue from the sale of biochar. A 1 MW reactor can produce approximately 2 tons of biochar a day.

Phoenix Energy has a 1 MW facility in Modesto that has recently been put into full operation and has several California biomass sites in the planning stages, including the proposed facility in Lake Tahoe, Wilseyville and North Fork.

A system similar to the one proposed here is being planned for North Fork and originally the Center for Biological Diversity opposed that facility, but withdrew their objections, largely because of the carbon sequestration associated with the biochar.  

From the Phoenix Energy About Us page:
"Phoenix Energy is a private label power company that builds, owns and operates on-site biomass gasification plants in partnership with businesses in the Agricultural, Waste, and Forestry industries.  Phoenix Energy helps its partners become their own energy provider, selling energy at retail rates."

Ideally the energy (electrical and heat) produced by the biomass reactor is used on site, and indeed the best payback is when a biomass facility is co-located with a facility that can utilize that energy, as the biomass generated energy is then replacing retail energy costs.  

If excess electrical energy is produced, the facility can be connected to the grid and revenue generated via a Feed In Tariff contract negotiated with PG&E or other local electrical energy provider to supply electricity at wholesale rates.  Fortunately, recently passed legislation, S.B 1122, allows for very favorable Feed In Tariff rates compared to those offered in the past.  If a favorable Feed In Tariff contract is established, we may also want to co-locate a large solar farm as a second step to reducing electricity costs and securing our energy supply in Mariposa.

In locating such a facility one not only needs to think about the area of vacant land necessary for storing the biomass materials.  The biomass from forest thinning projects will typically be chips, chipped at the removal site, trucked and then stored near the biomass reactor site. A large storage area is necessary to assure year around operation as forest thinning operations are most likely seasonal.  Approximately 10 acres of biomass storage space is required to support the continuous operation of a 1 MW biomass facility. A 1 MW facility could supply approximately 5% of the County's electrical needs.

While we are also looking at alternate sites, the County Solid Waste Facility and the adjacent industrial park would seem to be an ideal location for a biomass reactor and we have been in discussion with Greg Ollivier, the facility manager and County administrative staff regarding how such a biomass facility might fit into their short and longer-term plans.  The fact that a PG&E substation is located at the Solid Waste Facility also favors that site. Using the Solids Waste Facility as a gathering point for forest related biomass makes sense as that facility needs biomass-based carbon for their composting facility and there are currently large unused landfill areas available for biomass storage.

Build-able space at the landfill is in short supply, so the biomass reactor itself would likely be best located at the adjacent Industrial Park where ideally other industries that would benefit from access to low cost electricity and heat might also be located.  The location of a biomass facility in the County can be used to attract new industries and the related manufacturing jobs, thus expanding and diversifying the Mariposa economy.  A biomass facility is therefore a win for fire safely and forest health, a win for the local economy and a win for the environment.

1) From Wikipedia:  "The proposal that biomass is carbon-neutral put forward in the early 1990s has been superseded by more recent science that recognizes that mature, intact forests sequester carbon more effectively than cut-over areas. When a tree's carbon is released into the atmosphere in a single pulse, it contributes to climate change much more than woodland timber rotting slowly over decades. Current studies indicate that "even after 50 years the forest has not recovered to its initial carbon storage" and "the optimal strategy is likely to be protection of the standing forest".

2) Biomass gasification reactors can be optimized for either electricity production using higher temperatures or biochar using lower temperatures depending on the economics or goals of the facility.  The use of higher temperatures leads to conversion of more carbon in the wood to CO in the syngas which when burned produces more energy, but releases that carbon as CO2. The use of higher temperature pyrolysis, 900 to 1000 °C, produces a smaller quantity of a higher quality biochar that is more stable in the soil and more suitable to a wider range of applications. Phoenix energy has also found that use of a higher temperature pyrolysis minimizes the tar produced in the process thus minimizing maintenance costs.