Energy self-sufficiency and a new co-product opportunity is what biogas plant designer Krieg & Fischer has to offer. The German company is able to help ethanol plants use their thin vinasse for on-site energy and lower carbon intensity scores.
The ethanol industry is known for its co-products like corn oil and DDGS, but a company in Germany is giving them the opportunity to branch out into a new co-product: biogas. The German company Krieg & Fischer GmbH designs biogas plants worldwide for a wide variety of industries, from the potato industry to oil and gas companies. Krieg & Fischer’s expertise in established biogas technology is applied to the ethanol industry using fine vinasses as feedstock for biomethane production. Raphael Thies, managing director at Krieg & Fischer, describes the benefits, process and complexities of building a biogas plant.
Krieg & Fischer was launched 23 years ago in 1999. At first, their customers were mainly farmers, says Thies. The German Renewable Energy Act has generated a lot of interest in the farming community due to the incentives for energy using crops as feedstock. Over the years, Krieg & Fischer began building biogas plants internationally for a range of industries. “We know our different technologies in the field of biogas and our business [is] to adapt the technology to the raw material,” he explains. The company will design and build a biogas plant on site, regardless of which plant or farm will produce the feedstock.
Raw material analysis is where the work begins. Krieg & Fischer first built a biogas plant integrated with an ethanol plant in 2017 with an installation in Argentina. “At the very beginning, the idea was to digest corn silage, but our client realized quite quickly that he had a lot of organic waste from his ethanol plant and fine vinasse,” explains Thies. Krieg & Fischer then built the second biogas plant for the customer, this time using fine vinasse, which started operations in 2018. “When you produce alcohol from corn, you remove the carbohydrates to produce the alcohol and all the fats and proteins, and also still some carbohydrates are left. And the residues, all the vinasse… the usual treatment is solid/liquid separation. The solids go to farmers… for animal feed and the liquid part is a perfect substrate for biogas plants.
The fine plow as a feedstock for biogas is “fairly easy to handle”, says Thies. The advantage of fine vinasse is that it is already in liquid form, which facilitates its transport and the start of the anaerobic digestion process. Thin stillage comes out of the ethanol plant very hot, at 176 degrees Fahrenheit, so Krieg & Fischer solves this problem by cooling the stillage. “Then you have to carefully calculate the retention time in the digester tank, the organic loading rate and the main design parameters for each biogas plant,” says Thies. The more organic matter there is in the vinasse, the more biogas can be produced. The presence or absence of corn oil in the vinasse has an impact on the overall performance of the biogas plant. “But it doesn’t really matter, with or without corn oil, the difference is just the energy content,” says Thies. “Of course, when you take out the corn oil, there’s less energy in it, so you get less gas yield per cubic meter of thin stillage.” The amount of biogas produced depends greatly on the composition of the thin stillage, however, the biogas plant will typically produce around 600 to 1,000 cubic meters of biogas per ton of volatile solids.
Another important parameter is the type of oil removal technology used by the ethanol plant. Thies explains that if the plant uses technology that increases the dry matter in the fine vinasse, it can cause problems by increasing the concentration of nitrogen which inhibits the anaerobic digestion process. “When you increase the dry matter by evaporation and you don’t remove the nitrogen, the concentration in a certain amount of vinasse increases and then we could have a problem for the DA process itself because it will be an inhibition of bacteria from methane due to the high concentration of nitrogen,” he says.
Benefits of biogas
Biogas production offers many opportunities for ethanol producers, according to Thies. Ethanol producers can use the biogas or biomethane produced to generate renewable electricity or thermal energy to reduce their overall carbon intensity, he explains. The use of fine vinasses for the production of biogas can also bring independence to an ethanol producer. “The moment they need to find a customer for their vinasse, someone who buys it, corn oil depends on biodiesel producers, so if there’s less demand for biodiesel, the price will go down,” says Thies. “At the moment, they are dependent on other markets, [but] with the production of biomethane or biogas in their own factory, their own installation, they are [becoming] more independent of other parties.
Once the biogas plant is in place, the producer can rely on energy at a reliable price, without the need to rely on a volatile fossil fuel market. “It’s also a way to use King Corn. The last time I was in the United States, in South Dakota and Nebraska, a plant manager said to me, “I don’t know what will happen in five or ten years, what I’m sure is that right now we can grow maize.” ‘Maize will survive. The producer could also use other parts of the corn to increase the biogas yield, such as corn silage or corn stalks. Thies suggests that corn stalks are an ideal feedstock for an ethanol plant to use with fine stillage. Corn stalk would require a different pre-treatment technology to prepare it for anaerobic digestion.
The anatomy of a biogas plant
Although every biogas plant looks a little different due to different feedstocks, there are a few technologies that are consistent across the board. The most important of these, according to Thies, is the digester tank, which comes complete with a heating system, mixing system and insulation. Fine vinasse will be pumped into this tank from the ethanol plant. Anaerobic digestion takes place in this reservoir, when organic components are broken down into smaller chains, and then through acidification processes, specialized bacteria convert hydrogen and carbon dioxide into methane. “The main point is that you have to provide all the bacteria with the perfect conditions in terms of water content, temperature, and you have to homogenize that well,” says Thies.
After the digester, there is usually a secondary or “post digester” used to optimize biogas production. Next, a gas buffer system used to store the biogas for a few hours, Thies explains that this system is usually a plastic membrane system above the tank. “So of course you need a gas utilization system, a biogas cogeneration or upgrading unit or a biogas boiler where you can directly burn the gas so that it can produce electricity – so electrical energy, thermal energy or just biomethane that can be fed into a grid,” says Thies. An ethanol plant could have a biogas plant up and running in a year to 18 months Other factors, such as plant size or winter weather, could affect this timing.
The technology of a biogas plant is by no means in the research and development phase, explains Thies. “All this biogas technology [has been known for] over 40 years, the industrial scale we’re talking about now over 20 years, so it’s not R&D or anything like that. It’s a really well-established technology. There are a wide variety of plant sizes around the world, from those producing 50 cubic meters per hour of biogas to those producing over 6,000, these plants use proven technologies. Although the biogas industry started primarily in the agricultural market, with parts initially designed for construction or agriculture, it has grown to industrial size and has a lot to offer. “Now in Europe we have specialist companies providing the perfect technology for the different tasks: pumps, mixers, tanks, gas retention membranes, pre-treatment systems,” says Thies. “All this is no longer research and development, CHP units, 20 years ago it was an old truck engine and you tuned it. Now there are professional industrial suppliers.
Co-production of energy with ethanol helps plants have more stability and the flexibility of biogas gives ethanol producers more options for the future. “You can use it to heat your house, you can even use it to drive your car,” says Thies. “It can be used the same way natural gas is today.”
Author: Katie Schröder
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