August 2007 Mechanical Engineering Departments: Tech Focus, Pt. 2

This section was written by Executive Editor Harry Hutchinson.

Technology Focus part 2:
Fluid Handling and Fluid Power

Growing Interest in Algae

A developer of advanced technology ranging from unpiloted aircraft to nuclear radiation monitoring systems wants to be a partner in a not-for-profit group's experiment in growing algae as a source of motor fuel.

The company, General Atomics, has opened an office in Carlsbad, N.M., and said it plans to take part in research to develop biodiesel from algae. General Atomics said it expects to work with a Carlsbad-based organization, the Center of Excellence for Hazardous Materials Management, which is conducting studies at New Mexico State University into methods of cultivating algae.

The Center, known as CEHMM, studies a wide range of issues related to reducing the impact of hazardous materials on the environment. In one of its research projects, it has built outdoor ponds for growing saltwater microalgae at New Mexico State's Agricultural Science Center in Artesia.

CEHMM's executive director, Doug Lynn, said research began with bench-scale tests of cultivating algae in aquariums at Artesia and has progressed to five tanks ranging from 110 to 1,000 gallons each producing algae now. The next stage of research will use two "closed-loop, raceway-type ponds," each about an eighth of an acre in surface area, Lynn said. Each pond will be able to hold approximately 25,000 gallons of water.

General Atomics, based in San Diego, said it plans to work with the Center to develop processes for growing and extracting oil from the algae. The oil can be used to produce biodiesel, which can be substituted for petroleum-based diesel fuel.

According to Lynn, CEHMM does not yet have a contractual agreement with General Atomics.

Dave Hazlebeck, program manager for biofuels projects at General Atomics, said the company and CEHMM have been "talking together for about a year." Hazlebeck is listed as the inventor on a 2003 patent that covers a process to produce fuel from organic material. The patent assignee is General Atomics.

Two ponds at New Mexico State University's Agricultural Science Center are the next step in an experiment to cultivate algae for fuel. The research has drawn commercial interest.

According to Bill Davidson, General Atomics' vice president of advanced process systems, "We are very much intrigued by the potential that algae oils have, and so are the people at CEHMM."

Davidson said the office in Carlsbad is open now and is staffed by an engineer from Hazlebeck's staff.

Interest in biofuels has increased in recent years because it is hoped that they can reduce dependency on oil imports, and perhaps burn cleaner than fossil fuels.

The cultivation experiments in New Mexico are using brine algae that can tolerate the salty water of the Permian Basin. The ponds can be set on land not suitable for growing other crops.

The Basin is the remnant of an inland sea from Permian times, about 250 million years ago. The remains of the sea are locked under the ground of eastern New Mexico and western Texas. A spokesperson for CEHMM, Wren Stroud, said the current experiments use fresh water with salt added to approximate Permian water.

According to Lynn, the algae "are smaller than a human red blood cell." They have flagellae, which make them mobile, so they grow in the water and not only on the surface.

A paddle wheel, built by a local company, will keep the waters in each pond moving slowly to help keep the algae circulating. Circulation will assure that all the algae in each pool are exposed periodically to direct sunlight for proper photosynthesis. Although most details of the paddle wheel are proprietary, CEHMM said the wheel is made of a composite material to withstand the saltwater.

Lynn said that, based on results so far, researchers estimate that the algae can produce 4,000 gallons of oil per acre every year. CEHMM has experimental plots of canola at the agricultural center, and that crop may produce oil at a rate of 200 gallons per acre per year, Lynn said. Soybeans, another crop often mentioned in connection with biodiesel production, yield about 50 gallons of oil per acre every year.

The National Renewable Energy Laboratory studied algae as a possible source of jet fuel for many years. Bob McCormick, principal engineer at NREL, said the lab's research led to an estimate of 1,000 to 2,500 gallons of oil in a year from a one-acre pond. The program ended in 1996 because of budget cuts and changes in spending priorities, he said.

One of the key issues not resolved at that time was the technology to harvest oil from the algae on a commercial scale, he said.

According to the National Biodiesel Board, an industry-supported group that advocates for the use of biodiesel fuels, the most economical way to convert fat or oil into fuel is to react it with an alcohol that contains a catalyst, usually sodium or potassium hydroxide. The reaction causes glycerine to separate from the oil and leaves an alkyl ester, which is biodiesel.

Jenna Higgins, a spokesperson for the Board, said about one gallon of fuel is produced for each gallon of vegetable oil that enters the process.

General Atomics is also participating in a pilot project involving biodiesel for the Department of Defense. The project is examining the practicality of dissolving plastic waste with biodiesel to create an enriched fuel to run generators.

Rethinking the Matter of Diaphragm Pumps
by Alan S. Brown

Funny how engineers can keep improving a well-characterized product. Take the diaphragm pump, for example, which uses the displacement of a membrane to move air or liquids. It has been around since 1880, but engineers keep finding ways to make it better.

A case in point is the BTC series of small diaphragm pumps from Hargraves Technology Corp. of Mooresville, N.C. Hargraves got into the business when OEMs complained that pumps were usually the first component on a product to fail or require service. They not only wanted a pump to last 10,000 hours, but they wanted it smaller, quieter, more powerful, and able to handle hotter liquids.

This type of challenge often starts with materials. The diaphragm itself was the chief offender. Conventional rubber diaphragms of ethylene propylene diene monomer (EPDM) deformed easily for pumping, but began to wear out after approximately 3,000 hours.

Hargraves found a number of alternatives, including fluorocarbon (similar to Teflon), fluorocarbon-reinforced EPDM, and its own advanced EPDM formulation. The advanced EPDM lasted up to 10 times longer than conventional EPDM. It also deformed easily over a wide range of motion, so it could pump more fluid per cycle. "This increased the efficiency of our pumps to more than 70 percent, from 50 percent for most conventional diaphragm pumps," said the Hargraves business development director, Dan Schimelman.

More durable diaphragms illuminated another weak point in the design of diaphragm pumps: They are powered by brush dc motors. At best, the motor's brushes last for 6,000 hours before wearing out. This became a real issue after Hargraves switched to longer-lasting diaphragms.

Hargraves solved the problem by switching to small brushless motors. This eliminated the brushes entirely. The company also developed a proprietary bearing cage design to reduce radial loading. As a result, motors now last 10,000 to 20,000 hours or more.

"We've had some pumps that have lasted up to 70,000 hours, depending on application," Schimelman said.

Hargraves' diaphragm pumps come in several designs. The BTC series is a single-head miniature pump, and the BTC-IIS operates both pressure and vacuum with the same pump. The CTS Series is designed for very small spaces and lower flows, while the LTC Series is used in applications that require high efficiency.

Filtered Water Supply

The city of Waxahachie, Texas, has teamed with a neighboring utility district to prepare for water demands of the future. Waxahachie and its partner, Rockett Special Utility District, are taking bids for a new water treatment plant that, at least initially, will have four filtration trains using Memcor membrane filters from Siemens Water Technologies. The plant will be able to supply as many as 20.5 million gallons a day, which will be divided between Waxahachie and Rockett.

The city has more than 11,000 connections, and Rockett has just over 10,000 in several communities and in rural areas.

According to Kay Phillips, Rockett's general manager, the special utility district currently purchases water from Waxahachie and the city of Midlothian, Texas, for distribution to customers mostly in Ellis County and in some parts of Dallas County.

The special utility district was formed in the 1960s to distribute water to rural customers. Its primary business is retail sale of water to users, and it also sells wholesale to some municipalities, she said.

According to Waxahachie's director of utilities, David Bailey, the city has another plant in service, which was recently expanded to deliver up to 21 million gallons a day. That plant has potential for expansion to 27 mgd in the future, he said.

The city's expansion plans are due in part to an intention to sell water to new customers in Ellis County, according to Bailey.

The new water treatment plant, named for recently retired city manager Robert W. Sokoll, is also being designed with allowances for expansion. According to the project's lead engineer, David Gudal of Alan Plummer & Associates in Fort Worth, each filtration train in the plant has about 10 percent of its slots left open, where filters can be added in the future.

Bailey estimates that as many as five million gallons a day can be added to the plant's capacity by the installation of membranes in all the remaining slots.

The Sokoll plant will occupy part of a 38-acre site. The full site could hold a plant capable of treating an estimated 80 million gallons a day, Bailey said.

According to Phillips, the plant site is part of an 80-acre parcel owned by Rockett. Roughly half will be deeded to the joint-venture plant.

The Siemens membrane systems will filter water piped by Tarrant Regional Water District from two reservoirs, Cedar Creek and Richland-Chambers.

According to Siemens, the Memcor submerged membrane filters to be used at the Sokoll plant provide a physical barrier to bacteria and parasites, including Cryptospiridium and Giardia. The systems are completely automated.

Gudal said that the filters were selected in an earlier round of bidding and were chosen because they offered not only the lowest initial cost, but also came in lowest in a 10-year cost analysis.

According to Bailey, other features of the plant include on-site chlorine generation to eliminate the hazard of shipping chlorine. Water will be treated with ultraviolet light and hydrogen peroxide to control odor and taste.