Spent Coffee

October 10, 2004

Producers of soluble coffee generate waste that is an excellent boiler fuel.  As described in the February 20, 1997 Pressing News #56, "Coffee", traditional technology has been to press this waste, spent coffee grounds, as tight as possible and then burn it. This material, at 55% moisture, was burned in stoker grate furnaces.

Industrias Aliadas in Ibague, Colombia has added a twist to this technology. They dry the waste in a rotary drum dryer, to about 10% moisture. The resulting powder is then blown through 4" tubes into a refractory lined combustion chamber, where it burns in suspension. Excellent combustion occurs. Flue gasses from this chamber will provide the heat required by a new 18,000 pph boiler.

Until recently, Industrias Aliadas has processed 15 MTPD of "green" beans. These beans are first roasted, in twelve minute cycles, at temperatures of about 200o C. Next they are rapidly air-cooled and then flaked. The flakes are fed to GEA Niro extractors. The extractors, which run 400 kilo batches on a 40 minute cycle, are steam heated pressure vessels.

The coffee solubles are separated in the extractors. These solubles are then concentrated, either in an APV steam evaporator or in an ammonia cooled scraped surface heat exchanger. At this stage, the coffee concentrate is either bagged, in 50 kilo drums, for sale in liquid form, or it is directed to a spray dryer. The spray dryer is eight stories tall. The powdered instant coffee that we are all familiar with is the product of the spray dryer.

The 15 MTPD of beans at Industrias Aliadas results in 9 MTPD (60%) of waste coffee solids. These spent coffee grounds are diluted to about 85% moisture in the extractors. Currently this waste stream is drained a little and then directed into their rotary drum dryer.

An expansion to 45 MTPD is underway. As part of this project, a new Vincent VP-16 press is being built. This press will reduce the moisture content of the spent coffee from 85% to 60% moisture or less. The existing dryer will have ample capacity to further dry the waste to the 10% range required for burning in suspension.

The VP-16 provided is a successor to the traditional VP-16 screw press. The design retains the recognized high performance, with significant reductions in manufacturing cost. Coffee being a high torque application, the robust press will have a 30 hp motor driving the screw at only 9 rpm.

Issue 153