Improving the Efficiency of a Brewery's Cooling System
To reduce energy consumption and improve the performance of its beer cooling process, the Stroh Brewery Co. analyzed the glycol circulation system used for batch cooling of beer products at its Heileman Div. brewing facility in La Crosse, Wis. By simply reducing the diameter of the pump impeller and fully opening the discharge gate valve, cooling circulation system energy use was reduced by 50 percent, resulting in savings of $19,000 in the first year. With a cost of $1,500, this project realized a simple payback in about one month.
Project OverviewTo optimize performance of the plant's glycol cooling system, facility management at the La Crosse brewery hired a consulting engineering firm to perform a feasibility analysis and make performance optimization recommendations. This decision followed a p reliminary screening by the Energy Center of Wisconsin in Madison, Wis. The project called for the consultant to document the systems, analyze and evaluate the energy-saving opportunities, implement cost-effective projects, and conduct followup measureme n ts to confirm savings.
Brewing at the La Crosse facility is conducted on a weekly cycle beginning Sunday night, though not all tanks are cycled each week. After brewing is completed, the beer is cooled in a heat exchanger to 54oF (12 oC) and moved to storage tanks. The beer is further cooled in the storage tanks by a glycol cooling system. A solution of water and 36 percent propylene glycol is pumped through a 400-ton chiller that uses ammonia from the central refrigeration pl an t to cool the solution to 22 to 24oF (-5 to -4oC). The glycol solution then is channeled through an intricate piping and pumping system to cool the beer storage tanks. This pumping system was the focus of the energy-saving efforts.
The original glycol pumping system consisted of three parallel pumps, directly coupled to three 150 hp electric motors. Originally, each pump had a 17" impeller dia. Prior to this project, one impeller was trimmed to 14.75" dia. and its motor was r eplace d with a 75 hp unit. The 75 hp motor, however, could not handle the pumping load under all conditions; therefore, it was no longer in use. To compensate, one of the 150 hp pumps operated continuously. To prevent the motor from exceeding its rated a mps, the gate valve on the discharge was closed substantially.
Systems ApproachTo improve the energy efficiency and performance of its beer cooling system in an environmentally conscious manner, the Stroh Brewery project team developed a feasibility study based on the systems approach. The project consisted of the following eight st eps:
- Review system documentation, field verification and discussion of systems operation with brewery staff.
- Prepare a system detailed description.
- Prepare a measurement plan, identifying measurements (flow, temperature, press u re, kW, etc.) to be taken and under what conditions.
- Measure system operation according to the measurement plan.
- Evaluate current system performance by comparing measured data to design information (e.g., pump curves).
- Identify t ec hnical options to increase system efficiency and, if possible, ability to meet production needs.
- Analyze each technical option to establish feasibility, estimate cost and energy savings, and determine cost effectiveness.
- Prepare a repor t summarizing the results of the analysis.
Project ImplementationFollowing a thorough examination of the facility's glycol cooling system, three optimization measures were evaluated and considered for implementation:
- Trimming the pump impeller.
- Installing a new pump that matched the existing system.
- Installing a new pump with a variable speed drive.
Based on measured data and calculations, the team concluded that the first measure presented the greatest return for the least cost.
The project team used a seven-step procedure to trim the impeller. The steps, which took 15 hours to accomplish, were:
- Isolate pump and drain down casing.
- Remove top half casing.
- Remove rotor.
- Set up and trim impeller on shaft.
- Deburr and grind trailing edge of vanes.
- Balance rotor.
- Reassemble pump.
By trimming the impeller to 11.75", the discharge valve could be completely opened, and a normal constant flow rate, either equal to or greater than the flow rate achieved with a 150 hp motor and 17" dia. impeller, could be maintained.
ResultsField measurements conducted by brewery personnel after the impeller was trimmed to 11.75" dia. confirmed the success of the adjustment. Not only did the new system's flow rate increase by 15 percent, from 1,200 gal/min to 1,380 gal/min, but the smaller motor reduced electricity demand by more than 50 percent (from 112 kW to 54 kW). Extrapolating these results shows that the system's annual electricity consumption will fall from 981,000 kW-hr to an estimated 473,000 kW-hr.
Additional benefits realized by Stroh Brewery included: greater available cooling for peak load periods, extended equipment life and decreased maintenance for pumps and valves.
This Motor Challenge Showcase Project resulted in annual savings of $19,000, providing payback in one month. The Motor Challenge is a public-private initiative sponsored by the U.S. Department of Energy, Washington.
For more information, call (800) 862-2086 or visit www.eere.energy.gov/industry/.