Renewable fuels have long had a "green" characteristic associated with the environmental benefits of their use. With the rising cost of fossil fuel, renewable fuels now show a green economic benefit by lowering operating costs in industrial facilities with thermal processes. This article addresses and highlights the beneficial use of alternative fuels and the equipment modifications often required for renewable fuel use.

Fig. 1. LFG-capable furnace burner

Landfill gas (LFG) is created as solid waste decomposes in a landfill. This gas consists of about 50% methane, the primary component of natural gas, about 50% carbon dioxide and a small amount of non-methane organic compounds.

Renewable Fuel Opportunities

Instead of allowing LFG to escape into the air, it can be captured, converted and used as an energy source. The alternative use of LFG helps to reduce odors and other hazards associated with LFG emissions, and it helps prevent methane from migrating into the atmosphere and contributing to local smog and global climate change. Landfill gas is extracted from landfills using a series of wells and a blower/flare (or vacuum) system. This system directs the collected gas to a central point where it can be processed and treated, depending upon the ultimate use for the gas. From this point, the gas can be simply flared or used to generate electricity, replace fossil fuels in industrial and manufacturing operations, fuel greenhouse operations or be upgraded to pipeline-quality gas.

Pressurized methane gas can be piped underground and burned as a renewable fuel for manufacturing facilities at a lower cost than other fuels such as natural gas. In North America, and the United States specifically, landfill property that is in close proximity to manufacturing facilities can be a ready source of energy.

Given that all landfills generate methane, the beneficial use of LFG makes economic and social sense. Because methane is both potent and short-lived, reducing methane emissions from landfills is one of the best ways to achieve a near-term beneficial impact in mitigating global climate change. The greenhouse gas reduction benefits of using 1,000,000 btu/hour of LFG in a typical production facility are the equivalent of planting almost 1,200 acres of forest per year or removing the annual carbon dioxide emissions from more than 800 cars.1

Fig. 2. Burner with fuel orifice meter to measure LFG flow

Recognize Alternative Fuel Inconsistencies

Given its nature of formation and the variability between landfills, it is prudent to have an independent laboratory analyze the constituents of the gas as part of the initial project development. The lab analysis will provide an insight into the fuel characteristics and very often determine the scope and details of project requirements. In many instances, LFG contains one or more species of siloxanes. Siloxanes are nontoxic organosilicates that are used in many consumer and industrial products to enhance certain product characteristics. Organosilicates volatilize and are carried with the landfill gas as part of the organic decomposition process. As the LFG is combusted, the organosilicate reduces to silicon dioxide (SiO2), often creating deposits on the combustion and heat-transfer equipment. Siloxane filtration technology exists that will remove various siloxane species to below detection limits.

Identify Potential Processes in Your Facility

The most likely candidates for renewable fuel usage are those processes that have fairly consistent and continuous thermal-loading/fuel-usage profiles. Processes whose fuel consumption fluctuates due to changes in production, weather or other process characteristics will place a difficult demand on the supply of LFG from the landfill. LFG is typically produced on a 24/7 basis. Any fuel not used is generally flared at the landfill.

Fig. 3. Heavy-duty stainless shut-off valve used for LFG

Match Process Burner to Fuel Characteristics

The basic requirements of process burner design and operation include reliable ignition, flame stability and flame supervision. The fuel type can affect any or all of these requirements, so burners must be selected to match both the process and the fuel. Designers of thermal-processing equipment are familiar with the various types of burners and how to make the best selection to fit a particular process (Fig. 1). Few, however, are familiar with the special requirements of LFG. Because LFG is about half methane (the primary component of natural gas), not all natural-gas burners can fire LFG. Modifications, special selection, or at a minimum, special control and adjustment, are required to fire LFG. The burner manufacturer must confirm that the basic requirements of burner operation can be satisfied for a given LFG. Be sure to verify their historical LFG testing and experience.

From a given landfill, heating value (Btu per cubic foot), specific gravity (the mass compared to air) and corrosive-material content of LFG are nearly constant over time. However, these LFG characteristics will vary widely from one landfill to another. Not only will these LFG characteristics vary widely, but the gas conditioning will affect its characteristics. Gas conditioning includes cleaning or filtering, drying and transporting. While a thorough analysis is important to determine contaminants such as siloxanes, it is also necessary to determine the LFG combustion properties. With a specific gas analysis and knowledge of the process, a burner manufacturer can make the proper burner selection and determine what modifications are necessary for a particular fuel gas.

LFG commonly has low ppm (parts per million) concentration levels of corrosive material, particularly molecules containing sulfur. Depending on the ppm of sulfur-containing molecules, it might be necessary to select or construct burners, piping and control components of higher-grade materials such as high-grade stainless steel (Fig. 2). The presence of water and oxygen are factors that can increase the corrosive behavior of sulfur molecules, particularly hydrogen sulfide (H2S). Water can increase the rate of sulfur corrosion by more than 10 times. A good LFG supply should be dried well, but there is always the potential for some amount of water to be present. Compatibility of safety devices such as gas shut-off valves are the greatest concern (Fig. 3). While LFG installations often use burners with standard material construction or with minor upgrades, safety shut-off valves are commonly upgraded from those typically used with natural gas.

Another consideration when selecting a burner for LFG is gas-pressure requirement. LFG requires six to 20 times more pressure than natural gas across a fixed device (e.g. burner, valve or piping) depending on the quality of the fuel. Some burners can provide the same heat with LFG as with natural gas by simply increasing the gas pressure. Others enlarge the gas ports to take less pressure drop. Some styles de-rate the heat capacity of a given burner size, thus requiring larger burners or more burners to retrofit an installation designed to run on natural gas. Similar to burner sizing, gas-pressure requirements must be considered when sizing piping and control components. All components will take a higher pressure drop than natural gas for a given heat requirement. The pressure requirement of each component must be evaluated, but most components will typically be one pipe size larger than found on a natural-gas installation.

Gas flow must be determined to properly commission and adjust a burner. Because natural gas supplies, particularly in North America, are very consistent in Btu content and specific gravity, testing and publishing of gas-flow data for natural gas is practical. Gas-flow data for natural gas is typically well documented and expressed as gas pressure drop versus flow curves. However, LFG supplies are far less consistent. Therefore, one must rely on calculations or perform special tests to determine pressure drop versus flow data required to commission a burner on a specific LFG. For the most precise flow measurement and ease of burner adjustment, a fuel-metering device (e.g. an FOM, Fuel Orifice Meter) in the gas supply train is a worthwhile recommendation.

Make Back-up Plans for Your Production Requirements

In addition to process requirements, production requirements, schedules and down-time are also concerns when considering alternative renewable fuels. Back-up fuel systems can be considered and might be required. Many burners are capable of burning LFG and natural gas with minor burner or control adjustment. Usually manual control adjustment and switching of fuel supply is adequate. For the most demanding production schedules, however, systems exist to automatically switch fuels without manual intervention.

Economic Benefits

Renewable fuels such as landfill gas are typically procured from landfill operators on a long-term contractual basis. Many landfill operators use their gas to generate electricity on-site to sell green power to the local utilities, requiring a capital investment on their part. Selling the available landfill gas as a direct fuel replacement to natural gas requires the marriage of process opportunity and available fuel. This sort of partnership benefits both the process facility and the landfill operator on a long-term basis. Typically LFG supply contracts have a tiered fixed-price structure that enable many renewable fuel-conversion projects to be implemented with attractive, short investment payback periods of generally less than three years. Because of the fixed price advantage of LFG, the rising cost of natural gas only increases the relative savings for the plant and shortens the payback period. An investigation of what sort of renewable fuel is available near your facility is an excellent starting point. (Do not be daunted by distances. BMW (see sidebar) had a 9.5-mile pipeline constructed that crosses a river, two creeks, an interstate highway and their test track in order to deliver the available LFG to the Spartanburg facility.) Then have a detailed analysis of your process and production requirements done in order to determine the maximum beneficial use of alternative fuels and to secure the operating cost benefits for your facility. As companies begin to investigate, characterize and analyze their energy consumption, they will discover unknown profit possibilities. Improvements in energy usage and the associated environmental impacts are within reach today and can be enacted without sacrificing companies' economic well-being.

For more information:Contact: Gordon M. Harbison, C.E.M., Manager, Service Solutions, Dürr Systems, Inc., 40600 Plymouth Road, Plymouth, MI 48170; e-mail: gordon.harbison; or George Fritts, Product Manager, Low Temperature Products, Eclipse, Inc., 1665 Elmwood Road, Rockford, IL 61103;

Additional related information may be found by searching for these (and other) key words/terms via BNP Media LINX landfill gas, methane, furnace burner, natural gas, fuel orifice meter, renewable fuel

SIDEBAR: World's First Green Automotive Paint Shop

Four turbines at the Spartanburg, S.C., facility of BMW Manufacturing Co. LLC have been using "Green Energy" since January 2003 when BMW executed a long-term contract procuring Landfill Methane Gas (LFG) at a fixed cost from the Palmetto Landfill almost 10 miles away from the plant. The landfill, however, was capable of supplying BMW with more LFG than was being used to run the innovative cogeneration system that produces on-site power and generates hot and cold water.

In order to identify the potential for using the additional LFG as thermal energy in the paint-shop process equipment and eliminate the requirement for natural gas as a fuel, BMW worked in partnership with Dürr Systems, Inc., the supplier of the original process equipment. Dürr is also an Industry Partner in the Landfill Methane Outreach Program (LMOP) and experienced in applying renewable fuels in process equipment. The primary evaluation criteria for process equipment use was a consistent, year-round, thermal load/fuel usage and no potential for detrimental impact on the equipment or the painting process as a result of LFG combustion by-products. Process equipment and production uptime requirements also had to be considered.

During the summer of 2006, BMW Manufacturing became the first automotive company to use an alternative, renewable fuel to fuel its painting process equipment. All of the process equipment targeted for this landmark project had existing burners and gas trains that required replacement or modification in order for the burners to run on LFG. Twenty-three paint-shop process burners and safety valve trains were replaced in this project because of the lower BTU content of the LFG and the increased volumetric-flow requirements.

The Eclipse RatoAir burners installed by Dürr during this project did not change the thermal energy requirements of the process equipment. This additional use of methane in the BMW paint shop did not impact the production of electricity on site and has greatly reduced the paint shop's reliance on natural gas, providing financial benefits to BMW and significant environmental benefits to the surrounding community. Long dedicated to conservation, BMW's commitment to environmental responsibility is the driving force behind the development of this sort of environmentally friendly innovation.