Building biodiesel refineries

Making and designing systems and equipment

June 30, 2010

Crown Iron Works, Minn., was founded in 1878 as a blacksmithing shop. Today, one of Crown Iron Work’s business areas is designing and building production systems and plants for the biodiesel refinery industry.

If an image is not displayed, click the hyperlinked figure number to view it.

Crown Iron Works Co., Roseville, Minn., was founded in 1878 as a blacksmithing shop for the Minneapolis lumber, and flour mills.

As blacksmithing became obsolete, the company transitioned into ironworking and ornamental steel that defined the identity of a building. “It was what made the building what it was. You could see grating on a building in 1925 and say, ‘Oh, I know which building that is,’ by the way the ornamental steel made it look,” said Crown Iron Works Product Sales Manager Derek Masterson.

Eventually the ornamental steel business waned and the business morphed into a structural steel fabricator, Masterson said. Notable projects included many of Minneapolis’s signature skyways and the Metrodome. During World War II, the company supplied heavy industrial parts for ships, he said.

In the late 1940s, after the war had ended, Crown needed to find another source of work to replace the military contracts that had vanished with the war’s end. The company transitioned yet again, this time into an equipment manufacturer for the oilseed business. Oilseed is any seed or bean that yields vegetable oil or other fat. The company partnered with Iowa State University to develop a new way of extracting the oil from oilseed in the ‘80s.

In addition, it acquired the technology to engineer other aspects of oilseed processing—refining it from its crude form to an edible form, processing the byproduct glycerin, and processing biodiesel from the fat.

Today one of Crown Iron Works’ core business segments is designing and building production systems and plants for the biodiesel refinery industry.

The plants the company designs may process from a few million gallons of biodiesel a year to 100 million gallons a year.

The Biodiesel Refining Process

The biodiesel manufacturing process appears to be rather complicated and has many components
(see Figure 1). “But in chemistry terms, it’s very simple,” Masterson said. “It’s fat plus alcohol—in this case methanol—equals biodiesel plus glycerin.”

Crown Iron Works’ biodiesel production process uses a two-step transesterification reaction followed by neutralizing and washing steps:

There are two reactions and two separations, Masterson said. Methanol and a liquid catalyst are mixed with fat in a reactor and then pumped to a decanter (see lead image). After the biodiesel (methyl ester) is formed, the glycerin byproduct is separated from the biodiesel. The remaining biodiesel contains some fat that has not reacted, so for a second time, methanol and a catalyst are added and the mixture is reacted again and separated. The two-step transesterification reaction converts nearly 100 percent of the triglycerides in the oil or fat to biodiesel.

The process is an alkaline reaction, so once the second batch of glycerin is removed, acids are added to neutralize the process, Masterson said. In addition, water is added to flush out particles that should not be in the biodiesel. Then the water is separated from the methanol. Both the water and the methanol are recovered and reused. This makes sense from an economic as well as environmental standpoint, he said.

“Another thing that’s important about this process is that not only is it making biodiesel, it’s making the co-product glycerin in a standard crude form, as opposed to just getting rid of it as waste,” Masterson said.

At that point the biodiesel is chilled and filtered to remove contaminants that would otherwise clog vehicle filters or engines.

“So the chemistry’s easy, but doing it to high-quality standards, doing it efficiently, doing it economically and on a very large scale involves a lot of process engineering, figuring out the reactions and separations, and determining how much methanol must be added,” Masterson said (see Figure 2).

Challenges

One of the challenges unique to supplying equipment and engineering to the biodiesel refinery is ensuring safety because of the flammable and hazardous substances used to process it, Masterson said.

“Although it is possible to extract oil from oilseeds using physical pressure (screw pressing), the most effective way is a chemical process using hexane. But the hexane is highly flammable.”

Once the oil has been extracted, it is refined into biodiesel during another chemical process using methanol. Methanol is flammable as well as hazardous—both breathed as a vapor and to the touch.

“You go about designing a vegetable oil refinery one way, but you have to go about designing a plant that has explosive material in it another way,” Masterson said. Explosions and fires have occurred in biorefineries around the world, but they are mostly preventable with proper design,” he said.

“Because we are already familiar with that aspect of processing, it isn’t too much of a stretch for us. A lot of the equipment we design and manufacture is for condensing the methanol and recovering it to use again.”

Despite the flammability and hazardous substances issue, the processing equipment Crown designs and manufactures for biodiesel refining is similar to that used in most edible-oil processing equipment. “We use our engineering knowledge and design a process that works well with standard processing technology,” Masterson said.

Equipment. The production equipment the company uses for the process are reactors, decanters, surge and slurry tanks, tubes, and gravity feeders; plate and shell and tube heat exchangers; processing, washing, agitating, settling, filtering, and storage tanks; and pumps for transporting equipment. Virtually all the equipment is constructed of grade 304 or 316 stainless steel.

Some of the equipment is exposed to low-pH chemicals or sodium chloride, which is very abrasive, so many of the components are made out of 2205 or 2507 stainless steel, Masterson said.

“Also, because of the methanol, we use a lot of sealless pumps to prevent the possibility of methanol leaking from the seals. Instead of using a plate heat exchanger where methanol is present, we use a shell and tube heat exchanger so that there are no gaskets,” he said.

He added that the equipment does not have to be drastically altered to handle the process temperatures—which range from 140 to 300 degrees F—other than to make sure that the tanks are not overpressurized and to add a cooling jacket to some of the pumps.

Quality Standards. The final biodiesel product must achieve a quality specification—ASTM Intl. (U.S.), EN (European), or ANP (Brazilian) because when consumers want to buy fuel, gasoline or diesel, they just want it to work, Masterson said.

“That’s the whole deal behind why it’s so important for fuel to achieve a purity and quality standard, especially an additive fuel like biodiesel that usually is a component of a larger quantity of diesel—maybe it’s 2 percent, 5 percent. It needs to be the right quality so there aren’t any problems. It’s definitely a major goal of the biodiesel industry to make it transparent.”

That is why it is so important to make sure that all the fat has been fully processed. “If the fat has not been reacted enough, the residual fat will cause fueling problems, Masterson said.

Customers

Crown Iron Works has customers all over the world. “Wherever oilseeds are grown and refined, that’s a potential place for biodiesel,” Masterson said.

“Usually the oilseed refined into biodiesel is whatever is local. In the U.S. or South America, soybeans are the likely oilseed; in Europe, it’s rapeseed, which is canola in Canada; palm oil in Southeast Asia.

“There are certain things that you change for what we call the pretreatment. What we call pretreatment is getting the crude oil to a refined stage. In order to refine the oil, you basically make it bland and neutral. It’s almost like pure fat at that point.

“Any vegetable oil can be made into biodiesel at that point,” Masterson said. “The biodiesel equipment doesn’t really know or care where the feedstock came from.”

Farmer Cooperatives. Crown Iron Works’ customers are usually farmer co-ops, large multinational bioproducts corporations, or biodiesel start-ups.

The farmer co-ops are already in the vegetable oil business, Masterson said. “Let’s say they’re extracting oil from soybeans, refining it, and then they think, ‘Hey, let’s get into this sideline business called biodiesel.’ They already have the main parts of their business established, which is selling soybean meal, so selling the soybean oil byproduct as biodiesel is kind of a natural extension of their businesses.”

Multinationals. Another customer segment is large multinational food and agricultural producers like Cargill and ADM.

Exclusively Biodiesel. A third category of customers processes biodiesel as its sole product, Masterson said. “They may not have their own oil extraction plant. They may not have their own vegetable oil refinery. They’re just getting in at the later stages of vegetable oil processing right where the biodiesel’s made.”

However, usually the company’s customers are integrated before the biodiesel is made, or in some cases, integrated after the biodiesel is made, such as the fourth type of customer.

Petroleum Refineries. This category of customer may seem counterintuitive. “One large customer is actually a petroleum refinery. Petrobras, the state-owned petroleum refinery in Brazil, is an example of this type of customer, Masterson said (see Figures 3 and 4).

Although most petroleum companies would not be involved in the oilseed business, Petrobras is a clear exception. Petrobras has a history of partnering with local farmers for both food and social programs. Even though the company does not grow the soybeans, it can leverage efficiencies by maximizing usage of the petroleum refinery’s equipment. “By blending the biodiesel into the petroleum diesel, they add value and can save money by doing it themselves,” Masterson said.

Design Considerations

Crown engineers the plants to be relatively compact, while still allowing ample space for access. It uses gravity feed when appropriate, and orients the flow to take advantage of gravity and vertical alignment to minimize the need for pumps. “We try to make the best design as possible, with input from our customers,” Masterson said.

Although alternative fuels provide ample environmental benefits, the plants are held to cost expectations also. “We just try to make our equipment work correctly and be no more expensive than it has to be,” Masterson said.

“But the process technology and the equipment for the plant turn out to be a very small part of the overall cost,” Masterson said. “The machinery in a plant is important, but the building itself costs money, the laboratory, all the water treatment the storage tanks—that all costs money,” Masterson said. The feedstock and inputs—the fat, the methanol, other chemicals—are what drive the economics, but the operating cost of biodiesel refining and processing is primarily the cost of vegetable oil—85 to 90 percent of cost is the fats, Masterson said.“We’re not designing the chemistry. We’re designing engineering processes to make it work right.” Undoubtedly, the 132-year-old company is defining the identity of the biodiesel industry and making it what it is in the process.