For years, Murphy Brown, a subsidiary of Smithfield Foods and the largest producer of hogs in the USA, faced a major issue in its farming operations in Beaver County, Utah. At the time, it had been transferring all the hog manure to settlements tanks where it evaporated, thereby releasing harmful methane gas into the atmosphere in the process. But all that changed in 2012, when the farm’s operators embarked on an initiative that would not only capture those emissions for use as an energy source to power the facility but also reduce the impact on the environment.
Following are the specifics of how the project was developed, planned and, ultimately, executed:
Alpental Energy Partners of Provo was tapped to develop (and later operate) the Blue Mountain biogas generation plant. For the development of the Blue Mountain Biogas plant, Alpental Energy Partners — specialists in biogas and waste recovery — brought together experts who could evaluate the potential of using hog manure to generate electricity on a commercial basis and design, plus construct a state-of-the-art plant.
In order to build the plant in Utah, Alpental had to ensure that the liquid manure would not contaminate the groundwater supply or have an adverse impact on the air quality. To that end, Alpental brought in a local general contractor, Aqua Engineering, which specializes in the design of wastewater and effluent treatment facilities. As the production of methane gas as a fuel source is heavily dependent on proven sewage handling and anaerobic technologies, the project played to Aqua Engineering's strengths. In turn, the Salt Lake City- based company, which has considerable experience in the design of waste to energy projects that produce methane gas from bio-solids to generate both heat and power, brought in equipment specialists W-Cubed to help out.
From an equipment perspective, this particular project required special pumps that could handle the task. When it came to selecting the appropriate units for the Blue Mountain Biogas plant, Aqua Engineering looked to W-Cubed and KSB Inc. for technical assistance. According to Scott Rogers, Aqua Engineering's president, it was not disappointed.
"Aqua Engineering has enjoyed a long working relationship with W-Cubed, which has been the sales representative for pumps and mixer manufacturer KSB of many years standing," Rogers stated. "My company uses a large number of pumps, as it is highly active in the design and build of lift stations and pump stations. The ready availability of KSB submersible effluent pumps from W-Cubed, coupled with its ability to supply the pumps with panels, has led to us using KSB equipment for many of our projects."
High-performance pumps are only one aspect of the operation. As a high-capacity biogas operation, sufficient thought and consideration also went into other pieces of machinery. The Blue Mountain facility comprises waste treatment and anaerobic digesters, a gas scrubber and power generation hall. The plant specifications also called for powerful, small-blade mixers.
The conversion process
As with any bioenergy facility, the process begins with the feedstocks. In Blue Mountain's case, supply comes from 10 farms situated on the 1,000 acre site – an operation that produces around 1 million hogs a year. There is literally a constant stream of manure available for biogas production. At any one time, there can be as many as 220,000 hogs at Blue Mountain and in the event of manure being in short supply, there is always the adjacent Sky Line farm containing up to 280,000 hogs.
From there, the diluted manure from the finishing barns is brought to an influent basin (see Figure 1). From there it is transferred to a heat exchanger facility and then into two in-ground digesters. The resulting methane gas is vented into a scrubber tower where impurities are removed, and then moved into two gas compressors where the gas is dried and pressure boosted to feed a pair of 3520 1.6Mw Caterpillar engines.
The manure is mixed with water to reduce solids to between 2.5 and 5%. This slurry is constantly being pulled from pits adjacent to the barns and transferred to the collection stations at the biogas processing facility via a series of pump lift stations. Each collection station is equipped with KSB Amamix 2223/24UDG mixers and Amarex KRT vertical submersible effluent pumps.
KSB's Amamix submersible self-cleaning mixers are used extensively throughout the wastewater and effluent treatment industries and can be installed in virtually any application. The backswept impellers generate maximum thrust at minimum power consumption, and units can operate at up to 1700rpm. These mixers are activated prior to the pumps being switched on in order to keep the slurry in a homogenous state before it enters the central influent lagoon. On a typical day, the influent lagoon receives some 750,000 gallons of slurry.
"The purpose of the one-million gallon influent basin is to provide operational flexibility to the process," Brady Olson, vice president of Alpental Energy Partners, explained. "The process of draining the barns is a manual one, and it is necessary to feed the digesters with a constant flow of slurry that has a regular homogenous consistency. It means that the pits can be pulled when it is convenient to the operators."
For more on this story, including more details on the methane gas conversion process, look out for the March/April dual edition of Renewable Energy Focus magazine. Subscribe online today to receive your digital edition.