A New Wave in Grease

2012-06-08   来源：润滑油情报网 网友评论 0 条

History is fraught with stories of adversity turned into opportunity. Around the turn of the 20th Century, a fire in Ransom Eli Olds’ production facility destroyed his inventory of parts and vehicles, leaving him with only one unit of his then-famous “curved dash” automobile, which had been stored in his garage. Needing to fill orders for over two dozen vehicles but having no production facility, he contracted with various shops in Detroit. These shops in turn built components of his cars to the exact dimension of the one surviving vehicle.

   In effect, Olds created the concept of mass assembly, whereby accurately produced components of the car manufactured by different companies could be assembled in one place to make complete vehicles. (Henry Ford later would perfect the concept, adding conveyors and creating the mass production of vehicles.)

   Roughly a century after Olds’ ordeal, on March 20, 2007, a fire devastated the first fully biobased lubricants and grease manufacturing facility in the United States. Caused by a spill of heat transfer oil at the height of a grease reaction process, the fire at Environmental Lubricants Manufacturing Inc. basically destroyed the entire production facility in Plainfield, Iowa.

   ELM had been formed in 2000 to commercialize biobased lubricants and greases created at the University of Northern Iowa’s National Ag-Based Lubricants Center (UNI-NABL). At the time of the fire, ELM was listed by Inc. magazine as one of the 500 fastest-growing private companies in the United States. Like   Olds, the company managed to survive by contracting its biobased grease production to outside manufacturers until it could rebuild. As it designed a new plant in Grundy Center, Iowa, it resolved to seek alternative methods for making grease — without dangerous heat transfer fluids. UNI-NABL researchers also were searching for alternatives for heating biobased oils.

   In general, grease making involves neutralizing a fatty acid with a base, which results in soap and water. After the water is evaporated, oil can be blended into the hot soap. Grease therefore is basically soap which is mixed with lubricating oil, like a sponge with oil entrained in its cells. Completing the initial soap-reaction step, however, requires temperatures as high as 220 degrees C (428 F). Typically, electric power, gas or fuel oil is used to heat up a heat transfer oil, which is then pumped into the jackets of a vessel containing the products being reacted or “cooked.”

   UNI-NABL had begun experimenting with a small 1,750-watt household microwave to make 300-milliliter samples of soap and grease. Household microwaves, designed to maximize excitation of water molecules in foodstuffs, seemed to rapidly heat vegetable oils. UNI-NABL Associate Director Wes James said, “We did not know exactly why microwave is so effective for heating vegetable oils, but we were happy to see such a rapid heating process.”

   The concept of using microwaves for food and chemical processing is not new. In the early 1970s microwaves began to enter American households, promising speed in cooking and in thawing of frozen food. Industry, too,     began to explore the use of microwaves for processing. But for a long time the technology was relatively unknown, resulting in safety fears, and large-scale use was considered expensive.

   The technology now has progressed to the point of being reasonably foolproof in terms of safety, and the cost appears very competitive. In this approach, high-energy industrial microwaves can be daisy-chained at 75 kW each to provide as many kilowatts of microwave power to any liquid mass needing to be heated, including lubricating greases.  

   The UNI-NABL team sought out industrial microwave manufacturers and hooked up with AMTek, a company 60 miles away in Cedar Rapids, Iowa. Testing with two-gallon batches using a 75 kW industrial microwave proved to be effective. They also tested other properties, like the effect the shape of the vessel might have on energy absorption; different oil types and viscosities; mixtures of various oils, and more.  

   For example, to compare the effect of heating by microwave energy vs. conventional heating, a 300-ml sample of high-oleic vegetable oil was heated to 165 C (329 F) on a hotplate for six hours. A second sample of the same oil was heated by microwave to the same temperature, and maintained there by pulsing one minute of energy every five minutes for six hours. The two samples then were tested with an Oxidation Stability Instrument.

   Naturally, both oils oxidized due to extended exposure to heat, but the oil exposed to the hotplate had a change   in Oil Stability Index 2.5 times that of the oil heated by microwave. In other words, the oil heated with microwave energy showed less damage. Further work showed that these trials can be duplicated in larger quantities with higher levels of microwave energy.

   With these and other positive results, the researchers were on their way to scale up. In 2009, the University of Northern Iowa applied for a patent for the grease microwave heating technology   , and AMTek entered into an agreement with the university to pursue commercialization of the technology for processing chemicals, including greases. AMTek engineers involved the production staff of ELM and adapted an existing tank to make the first production quantity 800-gallon stainless-steel reactor.

   The results with the large-scale unit elated ELM staff. “We’ve made several batches of grease so far and they are as good and better than we had hoped for,” stated Alan Burgess, manager of operations. “The process is much faster, a lot safer and it seems like we are getting more complete reactions.”

   A programmable logic controller (PLC) is used to maintain the temperature of the product at precise degrees, thus ensuring a uniform reaction process every time. The operator simply sets the desired temperature, and the transmitters ramp down to a few kW power level as this target is approached. The PLC then continues to increase or decrease the energy input to maintain the target temperature.  

   Benefits are that the microwave transmitter unit can be installed anywhere in the plant, and the energy waves transferred to anywhere in the facility using special ductwork called “waveguides.” These are specially designed isolated tubes that convey the microwave energy to the grease reactor.

   “The footprint is relatively small, and there is no need for hot oil or oil reservoirs with burners, and there are no hot spots in the reactor,” Burgess noted. The two 75 kW microwave transmitters used for this project take less than 8 square feet of floor space, he added. “The energy goes directly to the product because there is no need to convert electric to thermal energy, nor to heat liquids that will transfer the heat using pipes or jackets on the mixing tanks.”

   The system has economic and safety benefits as well. Using microwave heating, ELM will need only a third of the time and energy compared to the conventional methods, Burgess said. “The safety aspects are evident because as soon as you shut the heating off, the     energy input stops immediately, eliminating other sources of heat and danger. And the system is designed in many ways that prevent microwaves from escaping into the plant.”

   “People have some general misconceptions about microwaves. We’ve seen a grant rejection, for example, because the reviewer thought that microwaves would cause arcs in a metal reactor,” Wes James remarked. “Microwaves can be applied to steel tanks, if designed properly to balance the microwave energy with the mass that is being heated. And any arcing can be detected, resulting in shutdown of the waves.”

   View-sights also can be installed in the reactor vessel, the same way home microwaves have a screened glass window in the unit’s door. These leak-free viewing ports can also be used for adding additives and oil if needed.  

   The team designed the reactor with the idea of eliminating the need for scrape surface agitation and possibly even eliminate mechanical mixing. A pump draws the contents from the bottom center of the tank, then circulates them back into the reactor from four jets placed on the reactor’s side walls. A small propeller built into the tank helps with mixing as the soap is forming.

   Other equipment, including pumps, mills and filtration systems, are the same as those used in conventional grease manufacturing.

   The first series of reactions used Lubrizol Corp.’s micron-particle size lithium hydroxide, which is emulsified in oil for ease of delivery. Previous laboratory testing had shown this particular lithium product did not result in foaming during reaction, and the reaction was very rapid.   Uniform microwave heating, in combination with the micron-size lithium hydroxide monohydrate, resulted in an extremely fast and complete reaction.

   Further economic analysis is under way to determine the cost benefits of this system compared to conventional heating methods. During the processes described here, the reactor was not insulated; the heat loss from the tank walls is expected to decrease with the addition of insulation. Even so, the temperature rise was approximately   3 degrees C per minute when the microwave power input was set to 120 kW. At about 8 cents per kilowatt-hour (the cost of electricity in Grundy Center, Iowa), the cost of running the two transmitters at 60 kW each is about $9.60 per hour, assuming 100 percent efficiency, and about $13/hour for about 75 percent efficiency.

   The goal now is to make more grease batches, to build experiential data that can be shared with others. A system that reduces production time and saves energy at the same time should have a positive impact on the competitiveness of the industry.