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Detecting Saving Potential Auxiliary Media: The Chemicals Industry's Under-Rated Cost Trap

| Author / Editor: Stefan Authier* / Wolfgang Ernhofer

Compressed air, Nitrogen & Co. are underrated cost drivers. When it comes to the saving of energy and subsequent costs in the chemical industry, the use of electricity and gas is the focal point. Use of auxiliary media such as pressured air, nitrogen or even water are seldom questioned. However, they deserve a closer look: the auxiliary media are pure energy and cost consumers.

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In the thicket of a plant, the true cost of auxiliary materials are not immediately visible. Systematic analysis can unveil astonishing saving potentials.
In the thicket of a plant, the true cost of auxiliary materials are not immediately visible. Systematic analysis can unveil astonishing saving potentials.
(Picture: Infraserv Gendorf)

Similar to water vapor, compressed air is an auxiliary medium which is indispensable in chemical plants and so is freely available everywhere. Thus, there is a definite risk in this fact: It is always the simple solution to use the available pressured air instead of searching for an alternative, for which we must use own devices in operations, which are to be maintained regularly and which have a definite failure risk.

Compressed air may be easily available, but its generation consumes a lot of energy. Finally more than 90 % of the used energy is lost through waste heat in the compressors. This example demonstrates how profitable the search for alternatives of compressed air can be: In a plant, a powdery substance is used from a product bunker in a Silo. During the construction of this plant, the pressured air is set to (6 bar), so as to accomplish this. However, it became clear during the energy optimization that the production volume flow can be reduced to one third as compared to the pressured air. For this, a simple fan is adequately sufficient. The solution is as simple as the energy saving was resounding. Through the fan, five million of standard cubic meter of pressured air can be reduced per year. The fan's power consumption is only 17 MWh per year.

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As water is very cheap it is mostly seen as a negligible factor, in which couple of cubic meters here and there do not really make much difference. However, this can lead to high follow-up costs: While the purchasing cost of water may be negligible, the treatment and disposal of water is much more expensive. In particular sewage treatment plants need a lot of energy, whether in pumps, agitators or fans. Each cubic meter of water that has not to be treated, thus saves power.

An example from the day-to-day operations illustrates the high saving potential in waste water treatment, even with the smallest of changes in process engineering. A company manufactures a powder, which is filtered at the end of the production from a sludgy mass. Subsequently salts must be washed out completely from the filter cakes, so as to guarantee the necessary product quality.

During the desalination process, demineralized water is used, which is purged in multiple stages in the filter cakes and thus, reduces the salt load step by step. Previously the washing water was discharged after each purging process and subsequently new demineralized water was used for the next stage.

Washing Water Replaces Reverse Osmosis

The analysis revealed that the washing water contained so little salt at the end of the purging process that it could be used without any problems for the pre-washing of the filter cake. Moreover, this change of procedure hardly involved any investments: Washing water from the last step just had to be captured in a new container. There it remains to be reused in the next washing process.

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