Sep 19, 2017

Pump Up the Grid

Scottish farms’ pasteurization process powers national grid

Pasteurization on a Scottish farm

Amixer and pump manufacturer’s new turnkey contract in Scotland highlights the increasing demand for ensiling and pasteurization equipment where there is a need to treat animal byproducts.

Fish morts used as feedstock for an expanding anaerobic digestion plant will be processed by equipment from Landia that includes an 8-cu-meter pasteurizer, which is fitted with a side-entry propeller mixer and dry-installed chopper pump.

A 10-cu-meter ensiling tank with an 18.5-kW stainless steel long shaft chopper pump also will be designed, manufactured, installed and commissioned by Landia’s team of engineers. This unit recirculates and blends the fish morts into a puree before discharging them into the pasteurizer.

With the fish morts suitably mixed, pumped and pasteurized at 70°C by the Landia equipment, gas yields are forecast to increase significantly at the anaerobic digestion plant.

Heat-Treat Organic Waste

This latest contract follows the installation of three Landia pasteurization systems, which help Shropshire Energy produce 2.5 MW of renewable energy at its anaerobic digestion plant in Littleport, Cambridgeshire, U.K.

The free-standing units heat-treat organic waste so the resulting thin substance can be used as an energy-efficient substrate. Each 8-cu-meter pasteurizer at Shropshire Energy is fitted with an 11-kW Landia chopper pump and a PODTR-I 4-kW Landia side-entry propeller mixer.

Organic waste received at 40°C is liquefied, then heated to 70°C, before the pasteurized matter is pumped back out as a valuable raw material in closed pipes to a buffer tank and then a separator. The finished digestate (8% dry solids) is approved to British Standards Institution Publicly Available Specification 110 for use as a nutrient-rich fertilizer.

“The pasteurizers work quietly and very efficiently, with quick batch times for the 100,000 tons-plus [per year] of organic waste that is processed. The pasteurizers’ pump and mixer are very reliable, meaning no downtime,” said Paul Davies of Landia.

Any surplus electricity generated from the anaerobic digestion operation is fed back to the national grid to power nearby homes and businesses.

Dynamic Organic Waste Management

Using pasteurizers to create renewable energy also has helped an organic dairy farmer in North Wales. When investing in anaerobic digestion to generate all of his heating and electricity, however, Richard Tomlinson set out to complement his farms’ organic milk production rather than create a rural power station.

Almost a decade on, under the umbrella of Farm Renewable Environmental Energy (Fre-energy), his closing of the loop comes in the shape of nine anaerobic plants that support the core business of farming. A key part of the successful operation has been the company’s patented de-gritting technology and the Landia pasteurization and pumping equipment. Combined with dynamic organic waste management and an efficient slurry management system, the results make a case for any dairy farmer with more than 300 cows to introduce an anaerobic digestion plant as the key to sustaining his or her business.

“FITS (Feed-in-Tariffs) is not our driver. We see the electricity, heat and fertilizer we produce as natural fit byproducts that, whilst not making headline figures, are now an integral part of our sustainable business,” said Chris Morris, Fre-energy technical director.

At Lodge Farm in Wrexham, U.K., the first of the nine Fre-energy sites, a separate lagoon was constructed within the larger storage lagoon to store the slurry and pump it underground to the digester 0.5 miles away every other week. This not only ensured the slurry would be delivered to the digester as fresh as possible, but provided a clean and convenient solution, rather than transporting the slurry by land.

In the reception pits at Lodge Farm, two 7.5-kW long-shaft chopper pumps with integral mixing nozzles chop and blend the tank’s contents, initially processing 25 tons of slurry per day from the organic dairy herd, as well as 6 tons of chicken litter per day before pumping the liquid into the 1,000-cu-meter digester.

In 2015, Lodge Farm became a licensed food waste site. Now, in addition to the farm wastes, materials from local food manufacturers and a nearby hotel are first treated by a 5-cu-meter pasteurizer hygienization unit tank that conforms with animal byproduct regulations. Designed with an integral heating jacket and an externally mounted side-entry propeller mixer and chopper pump to reduce particle sizes, the pasteurizer heats the liquid to the required 72°C for one-hour batch processes. There are no moving parts inside the pasteurizer, so there is no need to enter the tank for maintenance. There is also a 7.5-kW, 300-rpm submersible mixer in Fre-energy’s post-digestion store.

“Despite the high dry matter content, the Landia equipment works very well,” Morris said. “It’s simple, modular and it does the job, especially the ABP-approved pasteurizer, which is recognized by Natural Resource Wales and State Vet as a quality piece of kit. We like the side-entry mixer because it is both the manway and the mixer, reducing costs because only one aperture is required, rather than two.

“None of the Landia equipment requires intervention from us. It passes the test every time and very much fits in with what we do. Our [anaerobic digestion] process with our patented de-gritting system is also low on energy use. Our digester is mixed using less than 7 kW of pump capacity—running at only 30% duty—so only 2 kW of mixing energy is required for our 1,000-cu-meter digester.”

Morris said Landia’s service with the pumps also is a welcome source of comfort. “Landia understands what we are about, and when necessary, will roll up their sleeves to help us,” he said.

Based on the results in Wrexham, the pumps and mixers now strongly feature in Fre-energy’s expanding network of successful farm-based anaerobic digestion plants.

Little Bit, Long Way

Lodge Farm’s small-scale, non-headline, consistent energy generation is 160 kW of electricity and 200 kW of heat. Approximately 30 kW of electricity are used on site to power the engineering business, the Fre-energy office and the farmhouse, while around 60 kW of heat is used to heat the cow slurry and chicken litter in the digester up to 40°C. The rest is used to heat the house and office, with surplus electricity exported to the national grid.

Top-quality digestate is also a fundamental part of the Lodge Farm ethos. The digestate goes through a separator and then is stored in a lagoon with six-month storage capacity before being spread onto grassland.

The solid digestate, which contains a higher proportion of phosphate and potash, is transported by road to land used for growing winter crops to feed the dairy herd. Trials conducted by Bangor University have demonstrated that the biological oxygen demand of the digestate is reduced by up to 90%, representing a substantial benefit to the environment. It also has around 80% less odor than typical cow slurry, thus making the spreading of manures far more socially acceptable.

The commitment to the closed loop system begins right at the entry gates to Lodge Farm, which are powered by the AD outputs. In this part of North Wales there is conclusive proof that investing in anaerobic digestion can reduce carbon footprint and drive agriculture forward.

Kilowatts might not make the same eye-catching headlines as megawatts, but the simple and effective solutions in Wrexham represent next-generation agriculture that sets a great example. 

About the author

Chris French is a freelance writer on water, environment and renewable energy issues. French can be reached at [email protected].

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