Chapter 5: Biofuel Refinery Designs and Impacts
Unsurprisingly for what is, of course, an industrial product, many environmental impacts from biofuels arise from the design and management of the processing facilities. Plant design is a primary factor in determining the net energy benefit and up to 50% of the GHG impact. Biofuel refineries also have a range of traditional environmental problems, including water and air pollution. Finally, a major concern for facilities cited in dry agricultural regions is water use. However, with proper design and operation, biofuels refineries can be far more sustainable than petroleum refineries, which have tremendous environmental impacts themselves.
| Renewable Transport Fuel Obligation |
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| Another innovative way to promote sustainable biofuels in a comprehensive manner is the Renewable Transport Fuel Obligation in the UK. Similar to a renewable fuel standard, the Renewable Transport Fuel Obligation initially requires that 5% of road fuel come from renewable sources. To qualify for the mandate, the UK requires that biofuels meet both greenhouse gas and more general environmental and social sustainability requirements, including conservation of biodiversity, sustainable use of water resources, maintenance of soil fertility, good agricultural practices, appropriate land use, and support for workers’ rights.54 In order to develop and implement these requirements, the UK is first requiring mandatory reporting of GHG variables and sustainability indicators such as agricultural practices. For the first several years, biofuel producers will be required to submit these reports, but not meet any requirements. Then, based on the real-life data accumulated over this period, the UK will phase in mandatory standards. A key part of this process will be to develop standards that are applicable to a wide range of environments as the UK is expecting to import a substantial amount of feedstocks. This helps address one of the fundamental issues associated with evaluating biofuels, which is the lack of detailed information on what the social and environmental impacts of increased production will be. This approach has the advantage of developing requirements which are both clearly feasible and reflect the actual state of the industry. |
5.1
Ethanol Plants
5.1.1 Overview
There are two basic kinds of ethanol plants: wet mills and dry mills. Wet mills soak the corn grains in water and sulfuric acid to separate them into starch, germ, fiber and protein as precursors for making a range of products including gluten, high-fructose cornstarch, and other food products. Ethanol is also produced but is not the primary product of these kinds of mills. Dry mills begin the fermentation process by grinding dry grains and are primarily dedicated to ethanol production. Most new mills being built in the US are dry mills as they are less expensive.
Like any industrial facility, ethanol plants can produce a range of pollution, particularly if they are not properly monitored and held fully accountable to existing environmental standards. The range of problems that Iowa, home to the largest number of ethanol plants, is dealing with is indicative of this. From 2001-2007, Iowa had 397 instances of major pollution spills or violations of environmental regulations at ethanol plants. These covered a full range of air and water issues with a majority coming from failure to meet sewage pollution standards or standards for discharges into waterways. As a biofuel industry develops in Oregon it will be important to compile detailed information on all types of emissions and to carefully monitor impacts.
The biggest difference between ethanol plants in terms of their environmental impact is what energy source they use for heat and power generation. The second biggest factor has to do with the overall efficiency of energy use. There has been increased interest in using combined heat and power (CHP or cogeneration), where both electricity (which can be sold to the grid) and heat are produced as part of an integrated process. A CHP plant can improve overall energy efficiency by about 10%, and can be incorporated into plants using a variety of fuel types.
5.1.2 Natural gas-fired ethanol plants
The standard corn ethanol plant in the US uses natural gas for heat and grid electricity for power (similar to the wheat ethanol case examined in the section on net energy) and has an average capacity between 40 and 100 million gallons per year. These plants produce large quantities of distiller’s grains and drying the distiller’s grains for preservation and transport is also done with natural gas.
Greenhouse gas impacts: Natural gas is a relatively clean-burning fuel and most lifecycle GHG analyses of corn and wheat ethanol use natural gas as a model. A UC Berkeley study using Illinois corn and a baseline of 32.330 Btu of natural gas per gallon ethanol found that GHG emissions were 31% lower than gasoline at baseline,55 which is slightly better than the 18-29% average range for corn ethanol suggested by the National Renewable Energy Laboratory.
5.1.3 Coal-fired ethanol plants
As natural gas prices have risen there has been an increase in the construction of ethanol plants that can use less expensive coal.
Greenhouse gas impacts: Coal, which is mostly composed of carbon, is one of the leading sources of GHG emissions in the world, and one that may pose an even greater problem over the long-run as developing countries like China build coal-fired power plants to satisfy their electricity needs. Even with CHP (cogeneration), the UC Berkeley study calculated that emissions from coal-fired ethanol facilities wipe out any GHG gains from displacing gasoline with ethanol, meaning that ethanol produced from coal-fired facilities is just as bad as gasoline from a global warming perspective.56 Combining this with the serious environmental impacts that come from conventional grain production, particularly corn, coal-fired corn ethanol is an absolute loss from an environmental perspective. Ideally, coal-fired plants or ethanol produced in coal-fired plants would not be eligible for any state or local incentives. A good example of this in Oregon is legislation passed in 2007 which precludes coal-fueled ethanol and biodiesel production facilities from the state’s site certification exemption criteria.
5.1.4 Biomass-powered ethanol plants
It is possible to convert natural gas facilities to use biomass gasification systems for their heat generation. Gasification systems can be used to convert a wide range of cellulosic feedstocks into a clean burning syngas that can substitute for natural gas for heat generation. This allows the plant to be powered by corn stover, distiller’s grains, waste wood or other agricultural wastes that are available in the region. This not only reduces most of the need for fossil fuels, producing a greatly improved net energy balance, but also dramatically cuts GHG emissions. Ethanol from a Minnesota ethanol plant that uses biomass gasification was modeled to have a 53% reduction in GHG emissions.57 As mentioned previously, most cellulosic ethanol plants are being designed to use the large amount of leftover lignin produced to provide heat and power for the plant, in some cases even generating excess electricity to sell back to the grid. This accounts for a large portion of both their energy and GHG benefits in most calculations.
5.1.5 Biogas and integrated feedlots
The E3 Biofuels-Mead ethanol plant in Nebraska has pioneered another innovative way to reduce fossil fuel use and emissions from ethanol production. The plant is integrated with a cattle feedlot, which allows the wet distiller’s grain to be fed directly to the cattle without requiring energy-intensive drying. That alone reduces the energy requirements by nearly half. The manure and other waste products from the plant are put into an anaerobic digester to produce biogas, which is then used to provide heat for the plant. Without counting the avoided GHG emissions from the methane released by the manure (a major source of GHG emissions globally), ethanol from the plant was calculated to have 40% lower GHG emissions.58 On a less dramatic scale, many new mills are incorporating “bio-methanators,” which produce methane from wastewater in the ethanol plant to substitute for a portion of natural gas use.59
5.2 Biodiesel Plants
As biodiesel production is a far less heat- and energy-intensive process than grain ethanol, emissions from energy are much less of a problem. There are a range of innovative options for reducing the energy footprint of biodiesel even further, including using geothermal60 or other renewable power, or integrating biodiesel and ethanol facilities to better use excess heat and power produced from biomass firing.
| Policy Recommendations - Ethanol and Biodiesel Plants: |
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| State incentives to encourage the use of renewable energy and process efficiencies in new plants will pay substantial environmental dividends. Providing incentives for ethanol plants to employ biomass gasification would be a cost-effective way to reduce fossil fuels, promote real energy independence and reduce GHGs, while maximizing agricultural resources. (Financial incentives may be necessary because of the substantial up-front capital cost of biomass gasification systems.) There are a range of other process changes that can be utilized in first-generation plants to substantially improve energy efficiency, including not drying the distiller’s grains. The Pacific Ethanol plant in Boardman, Oregon is already moving in this direction. |
