The task

With around 7,300 employees, the Mayr-Melnhof Group is one of the world’s largest producers of recy-cled board and the leading manuf-acturer of folding boxes in Europe. The company‘s plant in Hirschwang, Austria, produces coated board for folding boxes based on wastepaper. Consequently it is confronted with the problem of disposing of the resi-dues (also known as “rejects”) from the processing of the wastepaper. Other byproducts arising at the plant are wood and sludge from the biolo-gical wastewater treatment plant.

Until the end of 2003, the rejects were still stored at the company’s own dump and sludges were dispo-sed of at external composting facili-ties. At the start of 2004, however, a law went into effect in Austria (and in Germany in June 2005) forbidding the dumping of rejects with a carbon content of more than 5%. This meant that an alternative solution was re-quired for using the residues arising, and Siemens was awarded the order to develop a power generating inci-neration plant to meet this need.

Customer Mayr-Melnhof board mill in Hirschwang, Austria

Implementation period January 2004 to March 2005

Scope of supply and services - Turnkey project - Processing and storage of residues - Metered incineration of combustible material - Ash discharge and storage - Steam generation, use of steam in the existing system - Flue gas purification - Engineering and commissioning - Complete electrical equipment and PCS7 process control system

Reject Power Plant

Pulp & Paper

Reference

From waste disposal to power generation SIPAPERCIS Reject Power at the Mayr-Melnhof board mill in Hirschwang, Austria

The solution

Siemens constructed a heat-recovery inci-neration plant for rejects with a capacity matched precisely to the quantities of combustible material arising in the plant. The heat from the incineration process is used to generate high-pressure steam, which is then used in the turbine to ge-nerate electricity. In addition to rejects and fiber material from pulp processing, primary sludges and biosludges from the company’s own wastewater treatment plant and wood waste can also be used as fuel. Moreover, the plant can process different fuel compositions and varying water contents in the fuel and adapt these automatically. The emission values comply with regulations and, as shown by a comparison of the airborne emis-sions actually achieved, are in fact well below the legal limits.

Incineration with impeller feedThe plant can be fired with three fuels si-multaneously in preselected proportions: rejects from wastepaper processing, wood waste, and sludge from the waste-water treatment process. For stoking, it is necessary to reduce the solid fuel in a shredder. The wood and reject fuels are

handled alternately, sieved and stored in a silo as processed fuel. Iron is sepa-rated before and after the shredder. An important added benefit of this type of handling is that the fuel is mixed, which makes it possible to even out chlorine peaks in the exhaust gas resulting from the combustion of PVC components in the fuel. In order to preselect the pro-portions of wood and rejects according to the availability of each particular fuel, the fuel components are metered separa-tely. Sludge, on the other hand, is pum-ped into the combustion chamber via a sludge pump without prior treatment.

Integrated flue gas purification systemThere were two reasons for the choice of the dry sorption process in the flue gas purification plant for precipitating acid components in the gas: the need to com-ply with the limits specified in the waste incineration regulations and the desire to minimize maintenance and operating costs. In this process, sodium hydrogen carbonate is used as a sorbent in the gas stream to bind the acid components, such as sodium sulfite, common salt, and sodium fluoride. A mixture of hearth

furnace coke and zeolites is also added in order to precipitate dioxins, furans, and mercury – substances that can then be bound adsorptively in the filter layer of the downstream filtration plant.

The result

Substitution of fossil fuels with rejects from the production process, which were largely of biogenic origin

Environment friendly incineration in compliance with strict emission regulations, as the plant operates in a protected water catchment zone that is a popular destination for daytrip- pers from the nearby city of Vienna

Substantial reduction in disposal costs

Use of rejects in an energy-optimized combined heat and power system

Avoidance of "waste tourism" by using rejects directly where the waste oc- curs

Incineration, burnout and steam generation at the residue incineration plant

©Siemens AG 2007 All Rights ReservedSubject to alteration

Siemens I&S IS E&C PPC P&P Dr. Hermann SchwarzP.O. Box 3240, D-91050 ErlangenPhone: +049 (9131) 7-42917 Fax.: +049 (9131) 7-25429 E-mail: hermann.hs.schwarz@siemens.com

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