Fiscalini Farms has a $4 million digester recently installed. This was be the first complete mix digester we saw that used cow manure as a substrate. The digester was built by Biogas Energy, Inc. from Germany. John Fiscalini kindly gave us a tour.
The process starts with cows. 1500 of them. This is a flush dairy, common on the West Coast where freezing isn’t a problem. The manure is flushed out of the stalls with water. The high liquid content (the dairy uses 1.2 million gallons of water per day to flush) has limited John’s choices in the types of digesters that would work at his dairy. RCM, he says, does not have a design that works on a flush dairy. In front of the digesters are a series of pits. I ask if these remove the grit from the waste. “No, they don’t remove the sand,” John replied. “They are supposed to remove the sand.” Not everything has worked according to plan. The digester was supposed to take outside waste such as FOG (fats, oils and grease) but the current permit only allows John to process waste generated onsite. The permit itself isn’t expensive (~$10,000) but dealing with the logistics and litigation has been.
The slope screen separator removes the solids from the flushed manure. The liquid falls through the cracks and is used later to flush the lanes of the dairy. The liquid is further removed from the solids via the press on the right.
The solids are left in a pile for a few days before a front-end loader picks up the solids and dumps them in the blue bin on the right. The bin weighs the solids and pushes the solids into the digesters via a series of augers. The digesters are loaded alternately for 60 minutes each with 4,000 lbs of solids added in a 60 minute cycle. The total solids of this digester seemed much higher than digesters we have previously visited and was 12% TS.
The high total solids seemed to be a requirement of the auger (see auger system above), not necessarily of the digester. There is a second influent stream dredged from the bottom of the pond out front which is higher in water content. No other liquid must be added to the digester. Each digester can hold 860,000 gallons.
The digester is complete mix run at 101˚F. The wall of the digester is concrete 14″ thick. This was over engineered, John says. The thickness was required to be earthquake proof, even though they never have earthquakes in the Modesto area. This is one of many things that increased the price from the quoted $2 million-ish to $4+ million with $1 million in grant funding from the CA Energy Commission.
Every valve, motor and sensor is connected to the programable logic circuit and can be viewed remotely as well. The designers in Germany actually look at the operation once a month and make suggestions to John on changes he can make that would improve operation. Sounds like a good company to work with. The digester also has a built-in H2S removal system. There is a net suspended in the head space that binds to sulfur. The net has a 20 year lifespan. H2S in the biogas is around 200-300 ppm. (John also mentioned a technology to inject ambient air into the top third of the digester so that aerobic bacteria consume the H2S. I will have to look into this.)
The biogas is pumped out of the digesters. The small pipe above goes to the flare and the large pipe goes to the generator. Today all of the biogas was going to the flare.
The heat from the generator is used to heat the digester. Even if the engine is down for a few days, the digesters hold enough heat to function correctly. When the plant was starting up, before there was biogas, John brought in a furnace to heat the digesters.
The Guascor generator turns the biogas into electricity and heat–more heat than John says they know what to do with. A Jenbacher made by GE was a another choice but that would cost 3 times as much. The third choice was Caterpillar but the company would not sell to John because of the emissions requirements of California. The Guascor generator is a 710kW engine though they only run it at 500kW and only 200kW is used on the farm. The rest is sold to the grid. The electric company pays $0.01 per kW more than the cost of electricity to consumers so that the company can meet their renewable energy quota. John said that fuel cells and microturbines will not work on dairy biogas.
Unfortunately, on the day we visited, the generator was not in operation because the intercooler for the generator’s turbocharger was clogged with mineral deposits. This is due to the hard water at the farm. The white clothes are covering the connections to the intercooler.
The heat exchanger in blue by Mueller sends hot water for heating and sterilizing needs to the cheese facilities.
The liquid from the digester is sent to a lagoon, which is fed into the canal and used to flush the stalls. John says that the farm has not needed to buy fertilizer for the crops for the last 20 years. The solids are dewatered and used as bedding for the cows.
John says that there is not a payback time for this digester unless he can get a permit to bring on off-site waste to increase biogas production 2-3 fold.
John said, “it is the right thing to do for the planet. We just need proper regulation.”
7206 Kiernan Ave.