Food ingredient manufacturer Penford Foods is reaping the rewards of a green energy project completed in late 2005 as a result of an energy usage study. Burns & McDonnell designed and built a first-of-its-kind industrial wastewater anaerobic digester gas utilization system.
The system uses the plant’s own biogas, produced by the anaerobic digester, as boiler fuel in a dual fuel boiler burner. What makes this system a first if its kind is its size (0 scfm minimum, 35 scfm average, 70 scfm peak) and lack of any storage volume for the biogas — the biogas is burned in the boiler at the widely variable rate it’s produced in the digester. Burns & McDonnell’s innovative yet simple system design eliminated the need for an expensive storage and compression system for the biogas. The simple payback is approximately three years. This new biogas combustion system is an exciting development in biogas utilization systems and opens the door for small and large green energy projects across public and private industry currently waste flaring this valuable resource.
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BioCycle magazine: Food Plant Puts 'Green Energy' Project in Place to Save Thousands in Fuel Costs
Energy Savings, Economic Viability
- Investment grade energy audit
- Conservation measures
- Project design, installation and performance measurement
The project involved the installation of two new boilers. The larger dual fuel boiler is a 2,700 MBH Bryan water tube boiler. The second, smaller, makeup boiler is a Bryan 1,200 MBH water tube boiler. The larger boiler operates as the lead boiler with digester gas as its first choice fuel. Both boilers are equipped with modulating linkage less state-of-the-art Weishaupt burners.
The custom PLC control system is the heart of the package. The Seimens PLC is programmed with a logic that automatically compensates for variable digester gas flow and variable steam header pressure. The digester gas flow varies as a function of the waste water flow and composition into the digester. The need for digester gas storage is eliminated by modulating the firing rate of the burner and combusting the digester gas as it’s produced.
The touch screen control panel includes color plots for nearly all system variables, including firing rate, steam header pressure and biogas pressure. Many other system variables for both boilers are also displayed on the color control panel.
Automatic fuel switching is also controlled by the custom PLC. The fuel is switched from digester gas to natural gas if either the steam header pressure drops below a set point for a period of time or the digester gas pressure drops below a set point while the burner is at low fire.
The system operating performance data are logged on an internal flash drive. All system operating parameters are logged on the flash drive and can be uploaded to a PC. This feature allows the operator to analyze and optimize the system performance.
- Dual fuel high pressure steam boiler with programmable logic controller-based (PLC-based) control system to provide boiler modulation based on biogas production and facilitate fuel switchover and boiler sequencing; uses a combination of biogas manifold pressure and steam manifold pressure to optimize use of available biogas, eliminating the need for onsite biogas compression and storage
- Natural gas-fired high pressure steam boiler
- Biogas piping system including condensate removal, flash-back protection and waste flare integration
- Control modifications to improve temperature and level control of existing anaerobic digester preacidification tank