Which came first, the chicken or the egg? It’s an age-old question that fascinates and encourages debate. Both are important staples for food cultures around the world, but what about all the waste? For years, poultry farmers in the Chesapeake Bay watershed have trucked manure to fields where it is used as a fertilizer. But a great concentration of animals means excess nutrient runoff that goes into streams and rivers and eventually ends up in the Chesapeake Bay. These nutrients increase the growth of algae and deplete oxygen that disrupts the aquatic ecosystem, making it difficult for marine life to survive.
In an effort to reduce the nutrient load that drains from a 64,000-mile area into the Chesapeake Bay, the Environmental Protection Agency (EPA) mandates an annual cap restricting the amount of nitrogen and phosphorous that can enter each tributary. And many states are challenged to stay beneath the cap. Here’s how Bühler Aeroglide supported a project that reduces the nutrient load by refining chicken manure into valuable products at the same time.
Hatching a Fuel Alternative
To address nutrient load, one of Pennsylvania’s largest egg production businesses partnered with EnergyWorks North America in Annapolis, MD. The result is a bioenergy program that uses gasification technology to transform egg layer manure into renewable energy and mineral byproducts, processing manure produced by five million layer hens. A Bühler Aeroglide high performance conveyor dryer is a key part of the process, used to reduce the moisture content of the manure prior to its gasification.
The processing takes place at the Gettysburg Energy and Nutrient Recovery Facility — the first of its kind in the U.S. - built near the chicken houses. The idea started with EnergyWorks and a need to understand the exhaust gases produced when drying egg layer manure. Drying trials conducted in Bühler Aeroglide’s technical lab helped engineers determine how to best configure the dryer.
“Processing engineers used small batches to capture exhaust levels that could be scaled up according to the amount of waste to process,” said Frank Rafter, global sales director for Bühler Aeroglide. “Initial trials established control levels that would achieve the desired environmental benefits.”
Pecking Away at Greenhouse Gases
The process begins with chicken manure that gets trucked to the processing facility and stored in a large pit. A system of conveyors brings manure from the pit through a low-pressure extruder that removes feathers and reconstitutes the product into uniform pellets. The pellets are then conveyed to an oscillating feeder designed by Bühler Aeroglide to distribute manure evenly across the bed of the dryer.
At this stage, the product’s characteristics require gentle handling to avoid fines. The product also requires low temperature drying and a long retention time to reduce the amount of ammonia lost in the drying cycle. Bühler Aeroglide’s AeroDry conveyor dryer was chosen for the application.
To meet the customer’s requirements, process engineers determined the dryer needed to remove water at a rate of 5775 lb/hr, and design parameters called for two scenarios. This was because egg layer manure tends to be drier in the summer and wetter in the winter. Bühler Aeroglide engineers provided one performance based on 26,000 lb/hr at 53% moisture that would yield 20,225 lb/hr at 40% moisture. Another performance was based on 21,000 lb/hr at 43% moisture that would yield 15,225 lb/hr at 20% moisture. The dryer evaporated the water using heat from steam coils.
“Engineers determined that a staged heating process would turn the manure into gas, while extracting nearly 94 percent of the nitrogen and almost 100 percent of the phosphorous,” said Patrick Thompson, EnergyWorks president and CEO. “The process also reduces ammonia pollution that releases into the atmosphere when manure sits for long periods of time.”
This was a major advancement toward a solution that had long challenged environmentalists, and it offered another benefit. “We could recover mineral byproducts and eliminate 34,000 tons of carbon dioxide (CO2) at the same time,” said Thompson. “The amount of carbon dioxide in the air contributes to the greenhouse effect which has reached an all time high. Creating a bioenergy program that reduces emissions at this level, while also reducing the nutrient load, was a significant accomplishment.”
The numbers speak for themselves. The bioenergy program reduces ammonia emissions by 50 percent, reduces manure storage by 97 percent and eliminates the annual hauling of more than 70,000 tons of manure that would normally be applied to 23,000 acres of land. Still, the project offers even more benefits that have far reaching implications for energy.
Producing Alternative Energy
After leaving the dryer, the product is conveyed through a discharge screw conveyor to another material handling system that gets conveyed to a large silo. The AeroDry dryer produces a hardened manure pellet that can stand up to the material process without generating significant fine material. The silo maintains a steady level of feed that fuels a gasifier, a thermal reactor that converts the dried chicken manure into a combustible syngas - a mixture of carbon dioxide, carbon monoxide, hydrogen, water, and small amounts of methane. Syngas combustion is completed in an oxidizer, generating heat in excess of 2200°F. This heat is used to produce steam in a heat recovery steam generator which drives a turbine generator to produce electricity. The power is exported from the plant onto the public power grid. The plant uses an enclosed condensate management system to achieve zero water discharge from power generation.
“We process approximately 240 tons of egg layer manure per day using a staged heating process,” said Patrick Topper, general manager of the Gettysburg Energy and Nutrient Recovery Facility. “The thermal-chemical process turns the manure into a gaseous fuel that produces alternative energy in a very efficient cycle.”
Interestingly, the heat produced from the gasifier has another valuable use. A portion of the steam generated in the boiler is fed back to the dryer as the heat source for manure drying. Condensate collected from the dryer is fed back into the overall enclosed loop. The result is an energy-efficient, odor-free operation.
An ‘Eggs in One Basket’ Strategy
But the program accomplishes much more than a nutrient load reduction for egg farming. The Gettysburg facility has a stream of revenue sources from the energy it produces. Electricity generated from syngas can be fed back into the power grid, and there are rewards for producing clean and sustainable energy. Utilities have quotas from the state and federal government that require a certain amount of energy comes from renewable sources.
“What we end up with is enough renewable thermal energy to power the plant and roughly 2500 homes,” said Topper. “We measure everything that comes into the plant and everything that comes out. We can say with certainty how much of a difference we’re making.”
The efficiencies of the Gettysburg facility have enabled it to participate in nutrient trading, a form of exchange that uses nutrient reduction ‘credits’ with a monetary value that can be paid to a seller who reduces nitrogen and phosphorous. It’s a market-based approach that allows a trade to take place between two sources, such as a wastewater treatment plant and a farming operation.
“The program is proving to be a successful way to improve water quality,” said Thompson. “We have an allowable pollution level and businesses can earn credits by reducing their pollution below the maximum allowed. We can then trade the credits with other businesses, those that aren’t able to make the same pollution reductions.”
Closing the Nutrient Cycle
A by-product of the manure heating process is a refined ash that contains valuable nutrients as feed or fertilizer.
“During the gasification process, nutrients are removed,” said Topper. “What’s left is a mineral compound that can be reused to restore soil. We can sell the phosphorous-rich ash to farmers who want to convert a Christmas tree farm to a soy bean field or reclaim an orchard that needs soil restoration.”
The ash also makes the perfect feed ingredient for agriculture with FDA approval, a year-long business enterprise compared to fertilizer that peaks with the seasons. This would mean the original egg layer manure could be recycled back where it came from, closing the nutrient cycle.
Promising Solutions for the Future
“The project offers a lot of promise for sustainable agriculture in Pennsylvania and beyond,” said Thompson. “Our long-term goal is to have zero emissions. No solid waste and no liquid discharge or air emissions. It’s a sustainable process that’s good for the ecosystem.”
Interpreting a customer’s vision and creating a drying solution is what Bühler Aeroglide does best, and its process and mechanical knowledge offers solutions in a wide variety of applications. New processes that support new products are born every day, and it all starts in the company’s tech lab.
“EnergyWorks needed a drying solution and needed to analyze the product’s exhaust before proceeding on a larger scale,” said Rafter. “We were able to support the customer’s vision to save energy and ultimately generate energy with a dried product. This is probably the biggest achievement of this project and one that we all enjoyed supporting.”
For more information on Bühler Aeroglide (Cary, NC), call 919-851-2000 or visit www.buhlergroup.com/drying.
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