New pumps increase US pig farm’s biogas yields

A ‘pioneering’ pig farm in North Carolina, US has reported a 10%+ increase in its biogas yields by investing in two new chopper pumps.

Soon after Butler Farms opened just over 25 years ago, the owner quickly wanted to reduce its environmental impact, culminating in the development of its own pig manure-powered biogas plant in 2011.

As a contract grower that takes 20,000 pigs per year, Butler Farms of Lillington, just south of Raleigh, has enough manure to warrant a one million-gallon storage lagoon turned anaerobic digester for the 10,000 gallons of manure that are produced daily.

“We may have started out in 1994 as a simple generic contract grower,” said owner Tom Butler, “but starting with improvements through the Environmental Protection Agency’s Clean Water Act, we wanted to do whatever we could to lessen our impact on the environment and our community.”

Consistently adopting best management practices for environmental improvements, Butler Farms chose to cover its pig waste lagoon in 2008 so that, as well as reducing odours, methane could be safely flared off, then three years later using that methane to generate biogas.

“It’s a never-ending process,” said Tom. “We’re pig farmers, not engineers or renewable experts, which is why perhaps we didn’t have the best mixing system for a biogas plant.”

Butler said the pressure ratios on the previous set-up, plus varying diameters of pipework, also put a strain on the biogas engine, but that Landia helped to optimise the system.

“Power isn’t always everything,” he said, “but our first mixers were so undersized. We’ve gone up from around just 10 HP to 60 HP, which means we can now move a million gallons whenever we want to; using two Landia chopper pumps at the start of the process and then just one is sufficient to keep everything moving.

“This is quite an achievement because our lagoon is rectangular, not round, but with two nozzles per pump, we are finally getting everything mixed properly, so it’s perhaps no surprise that we’re seeing such an increase in methane levels for our biogas plant, which will continue to improve as we fine-tune the operation.”

Butler Farms now generates more electricity than the farm needs through its 180 kW biogas-fuelled gen-set, so it has a power purchase agreement to sell the excess renewable energy to its power provider, South River Electric Membership Corp.

“Now that we have the right mixing system, our next step is to look at a more consistent supply of feedstock, because at the moment we have gaps, which we need to level out,” said Butler.

“Pigs of almost 300 lbs obviously produce much more manure than when they are less than 50 lbs, and we have turnaround times, of course, for cleaning before new stock arrives.

“So, we’re starting to look at introducing food waste, which again is why the Landia chopper pumps are such a good investment. We know that the equipment is more than capable of handling it. When we go ahead, we’re looking to add another Landia unit for our 20,000-gallon in-ground concrete intake tank, because again, the small existing pump won’t be able to handle the solids. A Landia pump will make sure that the consistency of the feedstock particle size will benefit our digester.”

A local cannery for sweet potatoes could soon become a regular (seasonal) supplier of additional feedstock for the biogas plant, but there is no shortage of enquiries from those wanting to find a home for food waste, according to Butler Farms.

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