Following the successful performance of its chopper pumps at a food waste to energy facility in Chino, California, full service environmental engineering consultant and contractor ES Engineering has introduced Landia’s GasMix system at the same site to help boost gas production from the facility’s two anaerobic digesters.
At the biogas facility that is capable of converting up to 200,000 gallons of liquid food waste per day to renewable energy, four 15,000 gallon tanks receive macerated commercial food waste from various sources. For the past six years, each tank has been served by a stainless steel Landia chopper pump that continuously reduces particle sizes and recirculates the tanks. A chopper pump and two submersible mixers from Landia are also installed in a 140,000 gallon equalization tank, which then feeds one of two 1.2 million gallon anaerobic digesters.
When ES Engineering began managing the Chino plant, the digesters were equipped with top-mounted propeller mixers, but as Plant Manager Alfredo Ferrin explains, the amount of mixing being achieved was insufficient:
“With California being the largest dairy state in the country, the site previously took in a large volume of farm slurry, but as many of these closed, so did the treatment plant (for three years). After the reopening, we soon realized that there was big room for improvement with the digester mixing”.
He added: “Our co-owners, a waste management company, have several large contracts with grocery stores and food producers for unwanted/expired products, so it was very important for us to maximize this large supply of feedstock with the right mixing system. It can vary from 10,000 gallons per day to as much as 200,000 – but on average it is 50,000 gallons per day. It was natural therefore that we consulted Landia, whose equipment had been doing a very good job mixing and pumping a wide variety of slurries with quite high levels of solids”.
Designed with an external chopping system that is separated from the pump casing and the impeller to prevent clogging, the Landia Chopper Pump (invented by the company back in 1950), can work as a standalone unit, but is also at the heart of the Landia GasMix system. All chopping is completed before the liquid enters the pump housing, which significantly reduces wear on the pump casing, impeller and sealing system.
“Apart from what you’d say was fair wear and tear, we’ve had no major problems with the Landia chopper pumps or mixers in six years” continued Alfredo, “so their durability and performance gave us the confidence to choose the GasMix system for our digester”.
Utilizing a combination of biogas and liquid recirculation for the mixing process to fully mix the digester and improve the quality of the biogas (which in turn can be used to increase power production), one of the major advantages of the Landia GasMix system is that all mechanical components are externally-mounted. This allows inspection and maintenance to be completed without having to enter or open the digester. In addition to the major health & safety advantages this provides – as well as no requirement for breathing apparatus or working at height, servicing of the Landia GasMix system can be completed while the biogas production continues uninterrupted.
Pipework is also usually mounted on the outside of the digester, but to suit ES Engineering’s requirements to have no further holes made in the wall of its insulated digesters during the retrofit, all stainless steel pipework was installed through existing manways.
“It is a big advantage to have the moving parts located outside the tanks,” added Alfredo, “and Landia were very flexible with their engineering skills to accommodate our needs for internal piping. Even allowing for the fact that the Landia GasMix had larger motors, we saw the difference straight away in the increase in biogas production. In fact, it increased so fast that we initially we had to stop running the site flare and switch the nozzles, but this was a good problem to have”.
The chopper pump that makes up part of the Landia GasMix draws sludge from the digester and pumps it through an aspirating venturi chamber. Biogas is then aspirated from the top of the digester, mixed with the sludge and injected into the tank. Powerful mixing performance is ensured in all areas of the tank by one or more ejector type nozzles and hydraulic mixing nozzles.
About a year later, when it was time to drain down the other digester at Chino for a service, the decision was made to also upgrade the mixing system in the second digester to Landia GasMix. The organic matter converted to methane by the two digesters produces 3.3 megawatts of electricity. This is ample to power everything on site and also sell surplus power to the grid.
“Before we switched to GasMix”, said Alfredo, “we would see floating matter on the top layer of the liquid, but all of the scum was soon broken down. It was clear that the whole tank was being mixed very thoroughly. Landia has also helped us with the parameters for timings and speed control so that we can control the energy costs. The Landia chopper pumps have been a great investment – and the GasMix system has made a very positive difference to our gas production”.
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