Zero Waste and Plant Optimization
When Pacific Biodiesel Technologies’ Big Island Biodiesel refinery came online last year, it was marketed as a state-of-the-art, zero-waste plant. The facility, scaled at 16,000 gallons a day, was Hawaii’s first since 2000 and boosted the state’s capacity by 500 percent. The phrase “zero waste” has gained popularity over the past year, perhaps as a result of Pacific Biodiesel’s marketing efforts, or maybe simply because it’s part of industry maturation to evolve beyond the inefficiencies of its legacy refineries. The term, however, means different things to different people. To Will Smith, engineering manager at Pacific Biodiesel responsible for process technology design and implementation at Big Island Biodiesel, being a zero-waste plant is not necessarily about being green or sustainable—although those attributes come as a nice added benefit. To him and others, it’s purely economical.
“Zero waste means we’ve made the necessary capital investments to eliminate all of the traditional waste products that can come out of a biodiesel process,” Smith says. And depending on the feedstock utilized at a particular plant, there can be a multitude of varying waste streams generated from virtually every stage of the process. Smith documented all possible waste streams from biodiesel processing and has developed a matrix he shared with Biodiesel Magazine identifying uses of those side stream waste products, from most to least favorable.
Feedstock refining or pretreatment produces several waste streams. If the plant is processing used cooking oil (UCO), there are wastewater and solids to contend with. The most favorable use of wastewater and solids from pretreatment of UCO, according to Smith, is anaerobic digestion, followed by composting and landfilling. Gums and foots are a side stream of oil degumming practices, and lecithin upgrading is preferred over selling direct to the feed market or, lastly, landfilling. Also, soapstock from caustic refining, spent bleaching clay and deodorizer distillate are more potential wastes generated from feedstock refining or pretreatment. The best route for soapstock would be to split to acid oil and esterify to biodiesel; second is direct sale of acid oil to feed markets. The clay can be composted or landfilled. Lastly, the best option for deodorizer distillate is selling for vitamin E recovery, or sold directly to feed markets.
The 1.5 MMgy Newport Biodiesel in Rhode Island, which collects UCO and refines to biodiesel, has been tagged a zero-waste plant, and Nat Harris, founder and production manager, shares with Biodiesel Magazine how his plant made the journey from paying disposal costs to finding added value in its waste. “Our food and water waste was something we would have a local septic hauler haul away, and we were charged money to dispose of it,” he says. But a fairly recent development in the past year or so has allowed Newport Biodiesel to turn that disposal cost into added value by selling its high BOD (biochemical oxygen demand) wastewater and food scraps from UCO pretreatment to an anaerobic digester in Maine. The UCO collected is comprised of 20 percent water. “It’s much better to realize a little bit of value,” he says, rather than paying someone to haul it away.
“There are various definitions as to what ‘zero-waste’ would be,” Smith says. “A lot of people would claim that they can get rid of a product at zero cost, so if someone will take it, it wouldn’t be a waste. The way I see it is, whatever leaves the plant has to have a real, marketable value—creating income from it, it has a market. I would say less than 20 percent of biodiesel plants today are zero waste. There are a lot of facilities that are generating coproducts they are disposing of, which, in my opinion, is a waste.”
From the core of a biodiesel refinery—the reaction and purification of fuel—several more waste streams exist. The best avenue for wet methanol would be in-house rectification and reuse, followed by marketing to an external refinery or, as a last resort, disposal as hazardous waste. In-house recovery of unrefined glycerin to refiner’s crude grade is optimal, Smith says, followed by marketing it to a refiner, then anaerobic digestion, and finally disposal as a hazardous waste. For saltwater and methanol from esterification, the best route, again, is in-house recovery and reuse or, as a second option, selling to an external refinery. For water-wash plants, spent water can be recycled and reused in-house, anaerobically digested or, at least value, disposed via the sewer system. Spent silicate from dry wash can be composted or landfilled. Spent ion exchange resins can be returned to the manufacturer for regeneration or landfilled, according to Smith, but Newport Biodiesel and its supplier have found another value-added use for spent resins. “We decided early on to go with ion exchange instead of water wash,” Harris says, thereby eliminating wash water going down the drain. When the resin is spent, the supplier takes the old resin and sells it to oil and gas drilling companies as hydraulic fracturing lubricant for wells. Finally, still bottoms from the distillation columns can be used in-house as fuel for process heat and steam, or sold as heater fuel to outside companies. Pacific Biodiesel’s Big Island plant employs distillation and uses its still bottoms to generate process heat and steam, helping offset the higher energy consumption of distillation.
“We’ve installed recovery and reprocessing equipment to utilize all of the side streams from biodiesel production on-site,” Smith says. “Methanol recovery, there’s removal of soaps and entrained esters. We take the glycerin—we call it the reactor bottoms—we take the material off the bottom of the reactors, the separator, we remove the soaps and entrained esters, and the esters are recycled into the biodiesel purification process, and the methanol is treated and recycled. The things you have to take into account are watching your capacity in biodiesel purification and reaction as well as the size of the methanol purification and recycling systems to make sure you can accommodate that extra recovered methanol. The facility is really designed from the get-go with this in mind, so it’s different than going back and retrofitting a plant to do the same thing.”
Waste streams from glycerin refining include salts, which can be used as fertilizer (best) or landfilled (worst), fatty acids that can be esterified to biodiesel and glycerin distillation foots, which can be sold to the feed market (best) or landfilled (worst). “A lot of biodiesel plants are producing glycerin with a high MONG (material organic non-glycerol) content, or it still has methanol in it,” Smith says. At Big Island Biodiesel, and the plants Pacific Biodiesel has built on the mainland, they produce glycerin that’s 85 percent pure. The methanol is recovered and treated, and pushed back into the process. “That’s typically not done,” Smith says. “It’s sold as a waste product or for very little value for upgrading.”
Derek Masterson, product sales manager with Crown Iron Works, says, “When we design a biodiesel plant, we follow the philosophy that we don’t want to discharge any water. We push any excess water into the glycerin for glycerin refining. You have a choice—you can make good biodiesel and pretty good glycerin or you can make biodiesel and shove all your problems in the glycerin, and we’re not about shoving the problems into the glycerin. We think that’s the wrong thing to do because then you have a poor-quality crude glycerin. So in the biodiesel plant, we’re trying to do a good job separating the biodiesel and the crude glycerin, recovering the methanol from the crude glycerin to end up with what I’d call ‘nice, crude glycerin.’ So out of that you’re going to end up with salts and a little bit of fatty acids and other organics and that could be 5 to 10 percent of your crude glycerin.”
“There’s a possibility to have a no-waste plant by just selling what you don’t need or throwing it into other products,” he says. “That’s been done for decades. I think the small producers are figuring out that they have small amounts of waste and it’s a good idea to do something with it, whereas on a large scale, those problems were already solved because they were such big problems that they have done something about it already. If you got a huge problem, you gotta take care of it. If you have a small problem, maybe you don’t.” Masterson says maybe plants that were inefficient before are becoming more efficient, and that waste streams may already be taken care of in certain process technologies themselves. Perhaps cruder technologies produce more waste that must find a home.
While sustainability is powerful, the motivators for zero-waste production are purely economic.
“Business can be sustainable and it can make economic sense to be that way—and maybe it makes more economic sense to be sustainable than to be otherwise,” Harris says. “It’s about minimizing or eliminating disposal costs, as well as the potential production upsets from not being able to find the appropriate markets or disposal routes for what would be considered waste,” Smith says. “All of the ‘wastes’ that are usually generated in biodiesel production, when recovered appropriately, are high-value products—we’re talking about fatty acids, or glycerin, or methanol or off-specification biodiesel. All of these products have markets either internally or externally. You’re looking at a cost savings when treated properly and upgraded. They’re no longer a waste product. So it’s very much an economic case to be made for being a zero-waste plant from an operational cost standpoint, and potential avoidance of shutdowns. That’s one of the things we’ve run across with biodiesel production the past four years. When they put in their plant they had a market for their glycerin when it came off the process, or their wastewater or solids that come off their pretreatment process. But then something happens to their buyer and they have to shut their plant down until they could find another market for it, which is obviously disruptive. So those are the two major reasons: a cost reduction or another profit center, as well as avoidance of shutdowns.”
Plant optimization is very closely intertwined with the concept of being a zero-waste producer, as both aim to increase margins and decrease wastes. Raj Mosali, president of Jatrodiesel, says producers rarely approach a process technology service provider and say, “I want to optimize my plant.” Rather, if a producer seeks feedstock flexibility, for example, a technology provider representative does a walk-through. “That’s when we notice optimization-related issues,” Mosali says, adding that it’s common for what is on the plant floor to differ from the piping and instrument diagrams. “We typically like to see the plant as it was built,” he says. He starts with the transesterification unit and works out from there, from the front to back. Once all that data is in-hand, plus knowing what feedstocks the plant will consume, they go one step at a time and develop a series of procedures required to optimize to perform at the specified volume. “Many times a plant is supposed to produce at one level, but it’s usually not because heat exchangers or condensers are not performing as they did upon installation,” he says. Cooling towers, boilers, water composition (soft enough?) and pumps are also checked. Pumps can decrease throughput for various reasons—additional piping or tees, or too much sediment in feedstock. “You design for 200 gallons per minute in the reactors and now if you’re at 150 gpm, this affects your whole reactor and the amount of time needed to finish,” Mosali says.
Rocky Costello of consulting firm R.C. Costello & Associates says an obvious technique is improving reaction. “You can improve it by using the Shockwave Power Reactor from Hydrodynamics to get more conversion,” he says. “The more conversion, the less likely you will need to distill the biodiesel, which is an expensive option in the first place. If you strip out the methanol, you’re in pretty good shape. People are touting distillation, and that’s a very expensive energy step. The sins of poor reaction—monos and diglycerides—are eliminated through that distillation process. If you have poor reaction, you can clean it up, but when you have really great conversion, say 99.9 percent, it’s not necessary.”
If a batch plant doesn’t want to move to continuous flow ultrasonics, though, Costello says, phase separate out the glycerin multiple times. “It’s a reversible reaction so as the glycerin remains, it prevents the reaction from going farther to the right,” he says. “As it’s eliminated, the reaction goes farther to the right and you have conversion.” He also recommends installing static mixers in line prior to the stir tank reactors to premix the oil and methoxide. “Those are ways to clearly improve your conversion.”
Many plants have already optimized to become feedstock flexible, but for those that haven’t, strong consideration should be given to do so. “If you have a plant that just has transesterification and you want to be more flexible, like our own BioFlex plant technology, we have degumming up front, esterification and traditional transesterification,” Costello says. “But there’s quite an expense to do that. On the other hand, it doesn’t mean that your transesterification unit that you originally started with has been optimized.” The add-ons for feedstock flexibility include degumming to remove phospholipids, and esterification that converts FFA to biodiesel and water. “Ultimately flexibility is important because it allows lower-cost feedstock, and what most clients tell me is their single largest expense is feedstock. It’s so expensive to the point that they’re not that concerned about energy. It’s getting cheap feedstock.”
Mosali says optimizing a multifeedstock plant involves a few key items. “One is, when the feedstock comes in make sure you know how much sediment and water you’re getting, and what the FFA concentration is,” he says. “The big problem with multifeedstock plants is sediment and water. What happens is, if you go with yellow grease versus corn oil from ethanol plants and animal fats, there’s a big fluctuation in the amounts of moisture and sediments that come in. Those are two big things, so if you address those on the frontend, then the rest of the process is very consistent, you don’t have to do anything major to change from one feedstock to the next, or a combination.”
Batch plant optimization differs from continuous flow plants by the sheer nature of its operations: repeatedly going full throttle and stopping. “Continuous flow is predictable and stays at one level all the time,” Mosali says. “In batch plants, you have to look at certain things because of the load fluctuations—pumps, reactors, boilers, cooling towers, chillers. Anything that’s running has that effect, so you need to make sure those load fluctuations don’t adversely affect that equipment.”
Mosali says one critical area where a lot of plants lose value is in lack of methanol recovery. He says typical return on investment from biodiesel and glycerin methanol recovery is six to eight months. “Some large customers don’t want to spend the money on energy to dry the methanol out, but there’s no other way,” he says. “It’s a one-time cost that pays you back in about six months.” Costello says methanol volume optimization to triglycerides is important, but tricky. “The more methanol you have, the higher conversion you have,” he says. “However, the more excess methanol you have, the more you’ll have to distill out at the end. You’re caught between a rock and a hard place. More methanol means better conversion, but more methanol means more energy to strip the methanol out of the biodiesel distillation column downstream. So many producers try pinching that methanol to the bare minimum, so that’s a suspect if there’s poor conversion. On the other hand, they may not have the capacity and distillation columns to strip out more methanol, so they’re pinched back for a reason.”
The tradeoff for better conversion is excess methanol in the reactors versus distillation capacity on the backend. “You have to strip the methanol out of the biodiesel or you won’t meet spec,” Costello says. “It’s optional on the glycerin. If you don’t remove the methanol from glycerin phase, that would be considered hazardous material, but if you have someone who could take it as a product, you can ship it on a bill of lading rather than on a hazardous waste manifest.”
Ultimately, Costello says, when it comes to plant optimization, most people have done a lot of the obvious; therefore, new opportunities and benefits lie in the unobvious, and for that, many producers should call on the assistance of process technology experts to identify them.
Author: Ron Kotrba
Editor, Biodiesel Magazine