Tannery Burns Fat, Cuts Emissions

The new steam-generation system at the Sudleder tannery consists of two 4,900-kW steam generators that are fueled by animal fat, a byproduct of the tanning process.

Workers at the Sudleder tannery, in Rehau, Germany, have been producing high-quality leather for more than 35 years, using a holistic approach that balances economy with ecology. The facility processes more than 3,000 hides/day, making the company one of Europe’s top tanners.

Producing such a large number of hides is energy intensive. The primary energy source is steam, which is used to heat water, dry leather, and maintain worker comfort in the production area. The fire-tube boiler plant that had produced steam for the facility for many years was inefficient, not environmentally friendly, and no longer able meet the steam demands of the dynamic company.

However, the answer wasn’t simply a matter of replacing the steam generators. Planners also wanted the system to be more environmentally friendly than the antiquated steam plant. The emission-reduction solution did not come from the usual team of science-and-technology experts. It came from the tannery’s maintenance team.

Maintenance workers suggested that, instead of burning fossil fuels, they should use the energy contained in the fat that is a byproduct of the tanning process. The fat is not only an energy source but the company had been, for years, paying to have the fat hauled off-site by a disposal company.

Rather than pay to have it hauled away, Sudleder maintenance professionals suggested byproduct animal fat be processed in this animal-fat and light-oil handling system and used to fuel the facility’s steam generators.

A feasibility study showed that using extracted animal fat from the subcutaneous connective tissue of raw hide (glue stock) not only reduced energy consumption but also minimized the company’s reliance on fossil fuels. The animal fat is considered to be carbon neutral and will actually produce considerably lower emission levels than normal fuel oil.

To put this idea into play, Sudleder installed a fat-extraction unit and two 4,900-kW steam generators, manufactured by Clayton Industries, City of Industry, CA (claytonindustries.com). To produce steam, feedwater is pumped into a single vertical continuous helical coil in the generators at a controlled rate. At the same time, hot combustion gases from the bottom-mounted burner pass heat upward over the coil, heating the water. This forced circulation produces steam efficiently and allows the system to respond faster to changes in demand than the old system.

In addition to burning fat, the two generators can also use natural gas or light oil as fuel sources. Changeover from one fuel to another happens automatically. Changeover also can be accomplished manually by using a touch-screen display on the control panel.

The generators provide additional benefits that were not part of the original plan. The compact vertical configuration takes up less floor space and makes it possible to use gravity to clean the heat-exchange surfaces by flushing them with water from top to bottom. This removes light deposits from the recovered fat that can form on the coil surfaces. Conventional boilers would require a complete drain, resulting in a large water loss.

Thanks to the maintenance team’s innovative thinking, Sudleder is now using an energy system that takes advantage of existing resources and decreases the company’s carbon footprint. Data, verified by an independent laboratory, indicate that CO₂ emissions have been lowered by 4,500 ton/yr. MT