The Economics and Environmental Impact of the Beneficial Use of Poultry Litter as Biomass Fuel

Industry practice for the removal of spent poultry litter has been the bulk spreading of the waste material over agricultural lands.  The intent of the land application of litter is the enrichment of soil with the nutrient laden material while concurrently providing a means of waste disposal for the poultry growers.  However, over application of litter in geographically concentrated areas has deteriorated environmental quality.  Poultry litter in bulk form tends to decompose rapidly, releasing soil nutrients.  When over applied, these water soluble or leachable nutrients are dissolved in rainwater which then flows into watersheds.  Nutrient rich run off water yields explosive algae growth, removing dissolved oxygen from streams and lakes, creating poor water quality and massive fish kills.  Although over application of poultry litter tends to be geographically concentrated, the areas of concern are occurring in several regions of the United States.

The United States Department of Energy (DOE) has five regional programs for the promotion of biomass as an alternative fuel.  These programs were initialized in response to the oil embargo of the mid-seventies to reduce our dependency on fossil fuel and advance the use of indigenous, renewable biomass fuels.  During 1997, the Southeast Regional Biomass Energy Program (SERBEP) of the DOE, as administered by the Tennessee Valley Authority, co-funded the demonstration testing of five biomass fuels with Primenergy.  One of the potential fuels selected by SERBEP was poultry litter.  The information contained in this document is the result of the tests performed by Primenergy under this co-funded effort and additional privately funded research.

Poultry litter is comprised of bedding material and bird droppings.  The bedding material comprises a major portion of the litter and is biomass; usually wood waste, rice hulls or other agricultural waste by-products.  As a potential biomass energy source, litter would initially appear to be a good candidate.  However, the chemistry of the droppings presents some unique combustion problems.  One of the primary soil nutrients in the droppings is phosphorus.  If the litter is burned at the elevated temperatures of an incinerator, phosphorus is released, forming phosphate salts and phosphoric acid.  Both of these chemicals cause significant metal deterioration and fouling in heat recovery boilers, thus rendering litter an unacceptable fuel source in conventional steam generation equipment.

Primenergy designs a unique energy conversion process called gasification.  The process of gasification is the thermal conversion of a solid biomass feed into a gas.  The intent and resultant process conditions of a gasifier are significantly different than an incinerator.  In an incinerator, the intent is to totally burn the solid feed within the confines of the incinerator.  The intent of a gasifier is to produce a gas for use exterior to the gasifier.  The advantages of gasification technology are that the lower operating temperatures vaporize less of the inorganic nutrients, i.e. phosphorus, potassium, etc., and the evolved gas exiting the gasifier can be dry scrubbed to remove any minor amounts of vaporized contaminants.

Primenergy’s gasification technology has been a commercially proven concept with both domestic and international installations.  Operating facilities range in capacity from thirty tons per day to over five hundred tons per day.  The energy output from the gasifier is used in a variety of industrial needs including hot air for material drying, process steam and the generation of electricity.

At its Tulsa location, Primenergy has a commercially sized demonstration gasifier with energy recovery equipment.  All of the testing of poultry litter as an alternative energy source has been performed at this location.  The standard protocol for testing of biomass materials includes an initial moisture content, elemental and ultimate chemical analyses of the feed material, air quality testing in accordance with US EPA standards during the demonstration testing and chemical testing of the ash generated from the gasification of the biomass.  Third party testing reports are maintained on file.  The proprietary data collected during the demonstration testing of poultry litter are the basis for sizing of energy generation equipment for industrial facilities. 

The demonstration testing of poultry litter was performed at a nominal rate of one ton per hour.  This rate is sufficient to predict process and environmental performances on much larger feed rates.  At this rate, Primenergy has established that the recoverable energy from bulk litter is approximately five thousand Btu’s per pound. 

Primenergy has established that gasification of natural, dry biomass feed stocks generates a gas suitable for firing in a prime mover such as an internal combustion engine or gas turbine.  Poultry litter, however, with its higher moisture, ash, nitrogen, phosphorous and sulfur contents, is not considered suitable for this method of energy recovery.  The high moisture and ash contents reduce the heating value of the generated gas below that which is required to fire an engine without auxiliary fuel (i.e. natural gas) support. 

In addition, poultry litter typically contains more than six times the amount of nitrogen of a natural biomass (three percent by weight versus one-half percent).  Therefore, unless scrubbed from the gas, the resulting high concentration of ammonia in the gasifier off gas will create an extremely high NOx emission rate in the engine exhaust.    High levels of NOx have been shown to cause smog and NOx emission rates are therefore regulated by environmental agencies such as the US EPA.  Sulfur and phosphorous compounds which evolve from the poultry litter must be near completely removed from the generated gas, since engine metal temperatures operate below the dew points of acids formed by these compounds..  Finally, liquid “blow down” from the scrubbing system must be treated prior to discharge or be disposed in a environmentally approved method.

Primenergy’s proposed method of energy recovery from poultry litter starts with dry, high temperature scrubbing of the generated gas, followed by firing in a heat recovery, steam generator to produce high pressure, superheated steam, which can be used to drive a steam turbine/generator.  Medium pressure steam extracted from the turbine can be used for process purposes.

The ash that is discharged during the gasification of poultry litter is odor free and biologically inert.  Analytical testing of the produced ash has revealed that, as predicted, essentially all of the inorganic soil nutrients and micro-nutrients remained in the ash.  In our search for an economically viable solution for the beneficial use of litter, Primenergy has demonstrated that the litter is an energy source and that the produced ash had the potential to be further refined into commercial quality granulated fertilizer.  If the litter ash fertilizer had economic value, then the ash can be exported from the areas of over application, providing a permanent and closed loop solution for the disposal of litter.  However, Primenergy’s business expertise is in process equipment, and not fertilizer.  This has led us to a corporation in Maryland whose primary business is the manufacture of capital equipment for the fertilizer industry.

Primenergy sent several hundred pounds of poultry litter ash to Maryland for evaluation as a granulated fertilizer. We were advised that, for commercial viability, any material must be reduced to a granule to allow commercial spreading.  The company contacted has several patents covering the processing of feed materials into fertilizer.  One of these patents details a process than can mix ash with other raw fertilizer ingredients, a binder and water to produce a granulated product.  Their independent research with litter ash proved that the ash could be refined into an excellent and marketable fertilizer with an initially estimated value of over one hundred dollars per ton.  The assumed value of the produced ash was over fifty dollars per ton.  This beneficial use of the ash not only adds a cash income and improved economic performance to the operation of a poultry litter to energy facility, but provides a means of exportation of the ash or local use through the displacement of imported phosphate fertilizers.

For the poultry industry, Primenergy proposes to provide energy generation on an industrial scale for consumption by poultry processing facilities.  These facilities are typically large consumers of natural gas and electrical energy.  The application of the technology of Primenergy and that of our corporate allies provides:

• Energy generation from an alternate, renewable fuel source which displaces energy generated by fossil fuels,
• A marketable and exportable commercial quality granulated fertilizer,
• An integrated facility that performs financially without heavy governmental subsidies,
• An avenue for the disposal of poultry litter that does not result in localized over-application of nutrient laden, odoriferous material.

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