Hog manure power
By Diane Mettler
By Diane Mettler
The Crone farm in Pennsylvania has
become a testing ground for a swine manure digester (with a 350 Chevy
engine power plant) and the results so far—in odor reduction and power
generation—have been encouraging.
The Crone farm in Pennsylvania has become a testing ground for a swine manure digester (with a 350 Chevy engine power plant) and the results so far—in odor reduction and power generation—have been encouraging.
Some projects take you places you hadn’t dreamed of. Take the Crone farm, for instance. Stan, Mary and their son Rich were expanding their Danville, Pennsylvania swine operation in 2003. They were in the process of building two, 2,200-head, self-sorting finishing barns when builder/designer Paul Schick of Schick Enterprises came up with a revolutionary waste collection plan.
Schick noticed a certain pig behavior consistent with this type of barn—dunging down the center, with the pigs resting along the sides. He realized that by taking advantage of that habit, he could design a waste system that would supply alternative energy, a supplemental income and produce less odor.
Schick’s plan was five, six-foot deep pits under each barn. Two strategically-placed pits would feed to a digester. Then once digested, manure would be returned to the other three pits in the barn for storage until the Crones were ready to spread. No additional post-digestion manure storage would be needed.
|Richard and Stanley Crone with Penn State’s Robb Meinen (from left to right). Once Penn State has completed a case study, the Crones will be looking at digesting more material and increasing the amount of power generated by their system.|
“The barns we were building were Sort All finishing barns, designed by Paul Schick,” explains Rich Crone. “Each barn had two rooms and in each room two pens, each holding roughly 550 pigs. There was a food court in the middle with the scales. We had to decide on Paul’s digester plan while we were building the barn because we would need to put in extra concrete walls.”
The Crones were primarily interested in the digester for odor control. “We live here. Just like the neighbors don’t want to smell it, we don’t want to smell it. We said, ‘We’ll experiment and be a guinea pig and do this thing.’ So we did.”
Skeptics said a digester system wouldn’t work with pig manure, but Schick knew he could design a workable digester. And the Crones began to talk to their local utility about getting their electricity onto the grid.
As the word got out about what was happening at the Crone farm, a variety of people and organizations wanted to see the project succeed, either because of its environmental benefits or because of the positive effects it could have on hog farming in Pennsylvania. Wenger Feeds helped pay for the reconfiguration of the floors and pits. Crone’s contractor, Countryview Family Farms, also put up some funds. Paul Schick told the folks at Penn State University and Professor Ken Kephart, Penn State’s swine specialist, received grant money from the Pennsylvania Department of Agriculture and the Department of Environmental Protection so the university could monitor the project. Even the local Sieple Environmental Trust, which donates to environmental projects, came forward. The remaining funds were financed through low interest loans from the Sustainable Energy Fund of Central Eastern Pennsylvania. The fund works to promote the use of renewable energy and clean energy technologies.
As the project moved forward, there were several unknowns that both the Crones and Penn State were watching closely. First, because this system was introducing biologically activated, digested manure back to the barn, would it affect the health of the pigs? Second, what about the methane coming off the digested manure? Was there a chance of blowing up the barn? Lastly, would the hydrogen sulfide and other gases emitted cause accelerated wear and tear on the equipment in the barns?
|Rich Crone (left) discusses carbon credits with Scott Subler, president of Environmental Credit Corp.|
“We wanted to make sure everything was being done because the Crones were going out on a limb here and doing something pretty innovative as far as digestion goes,” says Robb Meinen, senior extension associate with Penn State, who monitored the farm. “We wanted to make sure that the digester didn’t negatively affect them or their operation.”
Schick’s design turned out to be a 110,000-gallon circular, complete mix digester, 12 feet deep and 45 feet in diameter, with two compartments.
Under the barns, pits 2 and 4, positioned under the dunging pattern, collect the raw manure (approximately 78 percent) and feed the digester. “Each barn has a two-horsepower Zoeller submersible sewage pump,” explains Rich. “The collection pits from the barns are tied together with a 10-inch pipe and the manure is pumped up a hill to the digester.”
The digester is fed approximately 3,000 gallons a day—at eight intervals— over the course of a 24-hour day. “The tank would hold, if it was level, around 110,000 gallons,” says Rich. “But we keep it in the 85,000 to 90,000 gallon range—head space from the manure to the top of the wall.
“Inside the digester are two Houle agitation pumps, pumping through a manifold and injecting or circulating into different ports throughout the digester around the circular tank,” Rich adds. Then approximately 3,000 gallons a day gravity flow from the digester back to the barns.
“When the manure returns from the digester it feeds into pits 1, 3 and 5, which are also hooked together with a 10-inch pipe under the floor to keep them all the same level,” explains Rich. “The manure stays there until we can spread—usually once in the spring and then usually after we harvest.”
|For every ton of methane that the farm destroys burning in a flare, they receive a carbon credit.|
The Crones produce around 14,000 cubic feet of biogas per day, which runs a 47-kilowatt generator—a 350 Chevy engine. Any extra methane is sent to a flare. “Our generator is very small compared to what some of the dairies have. But our electrical needs are smaller too,” says Rich.
Although the system works fine now, it took 18 months to work out the bugs. The biggest issue they ran into was floating solids. “Most of the treatment practices that are out there with swine manure don’t experience the floating solids we have,” says Meinen. That answer was adding agitation—a five-horsepower Houle pit pump.
The local utility company also presented a setback. “When we first built the digester, we talked to them,” explains Rich. “We were originally going to power our barns and parallel the electric company. If we didn’t generate enough electric, the utility would fill in. However, when it came time to hook up, the utility didn’t agree to that arrangement.
“I don’t know if we didn’t ask the right question, or talk to the right person, or they just didn’t want to give us the right answer. But it’s been a long drawn out process,” Rich says. Today the digester subsidizes only some of their electric bill, but Rich is hopeful about “net metering” legislation being proposed.
Currently the Crones are producing about 550 kilowatts a day, about 50 to 60 percent of the capabilities of the setup. “We haven’t pushed it because I’m not getting enough value out of it,” says Rich. “But if net metering becomes available, it will be worth maximizing its production.”
The bag on the digester also caused them problems. Because the digester sits on a hill in a windy area, the constant gusts eventually caused a tear in the inflatable bag. The answer there was to build protection—a 60-foot by 50-foot building over the digester and a 16-foot by 16-foot square building alongside covering the generator.
Once the bugs were worked out of the system, everyone was pleased with the results. The health of the pigs hasn’t been compromised and the odor has been significantly reduced, both in the barn and during spreading.
|The Crone farm currently produces around 14,000 cubic feet of biogas per day, which runs a 47 kilowatt generator—a 350 Chevy engine.|
“Our conservation plan is no-till, and so we spread the manure using a 4,000-gallon vacuum truck and a 5,800-gallon Houle tank spreader,” says Rich. “You hear numbers like 70 or 80 or 90 percent less odor. I can’t put a number on it, but the odor is less.”
They are also pleased with the quality of methane from the digester. “Right now we’re running approximately 72 to 75 percent methane. And the more methane, the more you can run the engine.” says Rich happily. He also sees other future uses for the methane. “It just comes down to what’s economically feasible. You could bottle it and pressurize it. There are lots of things—it’s just deciding what you want to do.”
It also looks like through the course of the year the digester could produce enough electricity for the needs of the farm. “When we look at historical electrical usage of the barns we’re confident that we can meet the farm’s needs most days of the year,” says Meinen. “Electrical usage is highest in the summer and supplemental power from the grid will be needed on hot days. At cooler times we expect to produce a surplus.”
digester and associated facilities sit on a windy area—making the
digester bag subject to tears—so buildings were built both over the
digester and the generator.
And an unexpected added benefit has been carbon credits. “The Crones are the first farm in Pennsylvania, and the second hog farm nationally, to enroll carbon credits with the Chicago Climate Exchange,” says Meinen. “For every ton of methane that they destroy, either burning at a flare or in an engine and converting it to CO2, they get a credit. And that’s one credit they sell on the Chicago Climate Exchange. I don’t think they are interested in cashing them in right now. They are sort of doing a little speculation themselves.”
Once Penn State is finished with its case study, the Crones will be looking at digesting more material. “We’re running the digester at about half capacity. And I think we can almost double the size of our generator from what we’re running right now,” says Rich. “We can actually bring manure from other sources, liquid whey, food byproducts or whatever.”
It’s looking like this project will continue to take the Crones places of which they hadn’t dreamed.