fromstreamtostream

From stream to stream

World Water Day takes place every year on March 22nd. The commemoration day introduced in 1993 by the United Nations should remind people of the importance of water for humanity. All countries are called upon to carry out specific measures on the topic of water on this day. The 2014 motto is “Water and Energy”. The focus is on an important issue rarely discussed in public which emphasizes the connection between clean water and the growing energy requirements around the world. The chemical industry makes an important contribution to both.

Access to a safe water supply is a basic requirement for a dignified life which is not available in many regions of the world. Around a billion people, above all in Asia and Africa have no access to clean drinking water. According to experts the need for water will only continue to grow in the future. A growth in population of around 80 million people per year implies an estimated increase in water demand of 64 billion cubic meters yearly.

The outlook is similar with the supply of energy: 1.5 billion people have no access to electricity. The connection between water and energy is clear. Water plays an important role in the extraction of energy resources and equally in the generation of energy such as through hydropower, power stations and geothermal energy. In electricity and heat generation it serves as a driving force, for example, to move the blade wheels of the large turbines but also for cooling. Energy, on the other hand, is important for the processing and distribution for supply or irrigation in the countryside.

 Nothing flows without water

Industry is a large consumer of water. No matter whether for electricity generation from fossil fuels or nuclear energy, in the chemical industry, during paper manufacture or in the electronics sector. Even in the mining industry, the food industry, in steel production or in the automotive industry – nothing flows without water. More than 20 percent of the total water amount extracted globally is accounted for by process and industrial water for industrial use, surface water such as rivers and lakes and is also extracted from ground water.

In highly developed regions like Europe, it is even up to 60 percent, whilst the share of water used by industry in developing countries is only at close to eight percent. In Germany, even 84 percent of extracted water is used in the industrial sector. Again, thermal power stations use around three quarters of this, mainly for cooling purposes. To cover the electricity demand in Germany alone, around 630 liters of cooling water is required per person, per day, which nonetheless work for the most part in closed cycles and is recycled from time to time.

 Cool Water

III_1_WeltwassertagComplex chemical and mechanical preparation processes are required for the use of water as cooling water, service water or almost pure, completely demineralized water in a power station. For this the feed water is mostly softened and demineralized using ion exchange resins. This is necessary as the salts and alkalis contained in the water would otherwise accumulate as limescale on the heating surfaces due to the high temperatures in the power station and an insulating layer would build up which hinders the heat transfer. Due to this, thermal stress cracks or even the bursting of the boiler can occur and on the steam side, corrosion, abrasion and imbalance can occur in the turbines, for example. The processed water is subsequently fed into the condensing circuit of the power station. Within this circuit, the water is vaporized, used for electricity generation and re-condensed.

In some cases there is a second step downstream in the water processing – reverse osmosis – such as if the water contains a high proportion of organic substances. These substances would also lead to damage to the turbines and other components in the water-steam circuit.

Strong filter

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Thermal power station in Chemnitz, Germany

In the thermal power station in Chemnitz, Germany, for example, operated by the energy supplier eins energie in Sachsen GmbH & Co KG, LANXESS membrane filter elements significantly reduce fluctuations in water quality and filter out organic substances in particular. The 60 filter elements from the Lewabrane brand purify 50 to 60 cubic meters of pre-cleaned river water per hour for steam generator processes in the reverse osmosis procedure.

The power station takes the water for cooling processes and steam generation from the Chemnitz and Zschopau rivers. Depending on the particular purpose of use – as cooling water, service water or almost pure, demineralized water for steam generation – complex mechanical and chemical preparation processes are required. Despite softening and demineralizing with ion exchangers, the water still contains a high proportion of organic substances which can lead to excessive thermal conductivity and therefore to damage to the turbines and other components in the water-steam circuit. 90 percent of the input volume of water is used for the following processes as additional feed water.

 

IV_2_WeltwassertagThe goal predetermined by the operator of the power station to reduce organic impurities in the river water by 90 percent is met using this membrane technology. Yet reverse osmosis can do even more: For example it is suitable for demineralizing brackish water or salt water in order to obtain drinking water from it.

The ion exchange and reverse osmosis technologies complement each other and are therefore often combined to achieve optimum results.

Less water consumption through process optimization

Thanks to numerous changes to industrial production processes and constantly optimizing water processing, water consumption could be continuously reduced in the course of the years through multiple use. Products from the chemical industry have also made a decisive contribution to this.

For example, if water had been used 2.4 times during paper manufacturing in the mid-fifties, multiple usage would now be at twelve cycles. Nowadays, water is recycled an average of 28 times in the chemical industry before it is fed into the downstream treatment plant and purified again so it can be fed back into the water circuit.

However development is going even further. Because chemistry is a link between the raw material water and energy generation in two ways. Germany’s fourth biggest industrial sector not only supplies innovative approaches for efficient use of the raw material water but also solutions from energy generation that saves resources and is sustainable. This role will continue to gain in importance in the future.