Sarlin Balance helped reduce the need for spare units

The Salmisaari power plant in Helsinki dominates the scenery, although the enormous mountains of coal were hidden underground in a new storage area a couple of years ago.

The energy company for the Finnish capital, Helsingin Energia, has invested in environmental protection, reducing sulphur emissions by over 70% since 1990. This required, among other things, efficient sulphur removal.

Besides electricity, the power plant produces district heating at 300 MW and district cooling as a by-product of electricity production. The environmental impacts of the plant are continuously monitored, and the reporting requirements are stringent.

The sulphur removal system requires a lot of compressed air when it sprays lime into the flue gases.

The average compressed-air demand is 150 m³/min, nearly 80% of it in sulphur removal. The rest is instrument and working air for the ash conveyors, and dust removal by sound.

“The demand is not stable but fluctuates according to production. Including the stand-by compressors, the total capacity is nearly double, because we cannot compromise the production of electricity and heat in case of compressed-air system failure.”

“We also needed to improve the air availability in the plant because of a renewed environmental licence. If we cannot convey lime into the sulphur removal process at a sufficient rate, we shall have to run down our production.”

The compressed-air system is being renovated and upgraded step by step.

The compressor deliveries set the Sarlin compressed-air experts brainstorming. What they had seen and heard provoked an idea to modernise the plant.

“The plant featured several air networks and small machines with spare units in many places. The pipe lines were connected and the scattered compressors were brought under a common control and monitoring system, Sarlin Balance. The resulting compressed-air system is safe and easy to control.”

As Sarlin recommended, the old auxiliary boiler hall houses the new compressor station which was connected with the main sulphur removal compressors via a connecting pipe.

“This allows all the units to compress air for any point of use, which improves the reliability and reduces the need for spare units.”

The compressed-air plant was modernised with the help of Sarlin Balance. The entire air system with compressors and valves is connected with the control and monitoring system. The control room screen shows the operation, air production and pressure levels of all the units at a glance. It also helped to optimise the system. Compressed air is an expensive utility, especially if a high pressure level is maintained and many compressors run at partial loads.

“We have been able to drop the pressure level from 9 to approximately 8 bar without risking the sulphur removal process. A reduction of 0.1 bar at the current consumption rates already means savings of about 7,000 euros annually. Further benefits come from heat recovery from the air-cooled compressors in the new auxiliary boiler station; the heat is utilised for pre-heating the steam boiler combustion air.”