Südharzer Gipswerk GmbH has been producing special types of highquality gypsum for about 60 years in Sulzheim for the manufacture of ceramic moulds and chalk being sold worldwide. Furthermore, machine-applied gypsum, hand-applied gypsum and plasters for building and construction industry are part of the manufacturing programme. The annual total production of the factory in Sulzheim is about 150.000 tons. „We need compressed air for two application fields“, Works Manager Helmut Weiss comments. “For the control of our production facilities and for the pneumatic conveyance of our powdery products in our piping system”.

This conveying air has to meet two important conditions. It must be compressed oil-free to ensure high quality of the products. Special gypsum products require a constant compressed-air temperature of about 50 to 70 °C throughout the year. To generate this conveyance air the company applies positive displacement blowers locally installed on the factory premises. Two oil-free screw compressors and one positive displacement blower operate additionally in a central station for compressed air. All units were delivered by Aerzener Maschinenfabrik and part of them has been in use for more than 15 years.

Ideal adjustment

The central station is located in a close vicinity to a so-called source silo from which the powdery raw material is conveyed through piping to the individual further processing plants up to a distance of about 200 m. The oil-free compressed air is charged with max. 3 bar into the transmission pipeline.

Works manager Weiss comments: “ The whole trick is to adapt the volume of the compressed air as optimal as possible to the inlet volume of the gypsum of different bulk weight. The aim is to convey the largest possible volume of gypsum with the lowest possible volume of compressed air to the end of the piping.”

An oil-free and belt-driven screw compressor type VML 18 R of Aerzener Maschinenfabrik has been in operation since February 2008 in the central station for compressed air. This compressor unit of the new Delta Screw Generation 5 supplies an intake volume flow of approx. 1.000 Nm3 / h with discharge pressure of max. 3,0 bar (abs.). It is driven by an extraordinary energy-efficient motor, class EFF1 of 75 kW nominal capacity.

DELTA SCREW particularly suitable

The works manager Weiss still favours the machines of Aerzener Maschinenfabrik and does not look for an alternative: “We have been using Aerzener positive displacement blowers and screw compressors for more than 15 years in the field of pneumatic conveyance in our plant. We appreciate the high degree of professional competence of Aerzener staff, the customized realization of all projects and the high reliability of the products. Necessary service was always done to our complete satisfaction. DELTA SCREW Generation 5 is particularly suitable in view of the small space in our station as the compressors have a slender and compact design and can be installed wall-to-wall”.

Workshop foreman Anton Konrad appreciates that beneath the reliability are the low maintenance costs of all Aerzener machines. Current checks and “normal” maintenance is done by own staff but general overhaul is done by Aerzener staff. It has not been necessary to replace essential or expensive components even after operating times of 75.000 h.

Customized unit

The new Aerzen Screw compressor VML 18 R G5 delivers continuously the stipulated compressed-air volume with a max. pressure of 3,0 bar. The unit was matched exactly to the requirements of the conveying system in Sulzheim by means of a detailed design. An overflow regulator opens as soon as the set pressure in the connected system is exceeded and guarantees the required continuity of the pneumatic conveying under optimal conditions. So the compressor does not switch off after reaching the stipulated discharge pressure, as in case of pneumatic conveying the material in the piping system would deposit immediately and block the pipes. The overflow regulator works with extremely high regulating accuracy, short response time and independent from auxiliary energy by means of an admission-pressure controlled diaphragm drive.

The compressor is shut-down automatically, as soon as the current silo has been filled and the corresponding pipe has been blown clean. The compressor unit is monitored by a central line control station.

Precision landing

!We use 99,5 % of the generated conveying air for conveying. Only 0,5 % is blown off into the atmosphere to keep the pressure level constant. This is an optimal result”, Works Manager Weiss is very pleased. “The specialists of Aerzener Maschinenfabrik supplied a customized, energyoptimized compressor. We reached our aim to transport as much material as possible with as few compressed air as possible with a precision landing.”