European Chlorine Industry under Change – Challenges in Brine Treatment

European Chlorine Industry under Change – Challenges in Brine Treatment

The European chlorine industry is currently undergoing major changes. For decades mercury based electrolysis cells have been the technology of choice for the production of chlorine and caustic. The rate of conversion from the mercury cell to the membrane process will further increase due to the implementation of the chlor-alkali BAT (Best Available Technology) conclusions under the Industrial Emissions Directive. The Directive requires implementation of the chlor-alkali BAT by member states by the end of 2017.

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Mercury Cells

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Membrane Cells

No Time to waste

Several plants continue the progressive conversion to the membrane process, which now represents about 61% of the chlorine production capacity in Europe according to Euro Chlor’s latest Industry Review. In contrast, the mercury process now accounts for apprUntitled4oximately 23% of production capacity, representing as much as 2.75 million tons per annum (MTPA) of chlorine.

While some countries are almost mercury free (Italy, Netherlands, Norway) others still have major challenges ahead (Belgium, Czech Republic, France, Germany, Hungary, Spain and others). Industry specialists expect that an extension to the 2017 deadline will not be justifiable due to the relatively long lead time (the mercury ban was published by the European Commission as early as 2013). With only two years remaining, it is crucial that serious consideration be given to efficient conversion solutions, including the necessary upgrading of brine treatment and filtration technology.

Brine TreatmentUntitled3 and Filtration

The FUNDABAC® and CONTIBAC® Filter has established itself as the de-facto global standard for the treatment of brine in the chlor-alkali industry. The unique features and benefits of these filtration systems contribute to significant process improvements as well as a reduction in operating and maintenance costs. All components in contact with the process fluid are made from chemically resistant plastic materials. The internal components of the filter are constructed from high strength extruded and molded engineered plastics, designed for a long lifetime under harsh conditions. Fine filter membranes assure an excellent brine quality. The membrane media are secured tightly over the filter elements, effectively preventing leakage. In contrast to competing filtration systems, DrM filter internals do not need to be replaced during maintenance. This significantly reduces waste and maintenance costs compared to competitive designs. The filter uses a very efficient back-pulse system characterized by high pulse pressure and a dynamic cleaning effect. Irreversible blinding of the filter media can be prevented and acid-cleaning cycles can be significantly reduced or avoided completely.

The Burden of Mercury Removal

Mercury deposits formed over years do not disappear overnight. Conversion plants are confronted with the removal of significant quantities of mercury for prolonged periods. Efficient Hg removal from the brine circuit down to the low 2-digit ppb level is crucial for the membrane cells.Untitled6

A straightforward method is to precipitatemetallic Hg with NaHS to form HgS, a very fine insoluble particle that can be filtered out. DrM can demonstrate extensive experience with HgS filtration where the efficient back-pulse system is key to a successful operation. Once mercury is eliminated from the circuit, the filter continues to serve as brine polishing unit without modification.

Safe Handling of Hazardous Chemicals

In the aftermath of the explosions at the port of Tianjin China and at a chemical plant in Shandong, we are once again reminded of the reality of the dangers involved in handlingfig1 combustible and toxic chemicals. When running an automated production facility with a team of experienced operators, risks of incidents can be minimized. This having been said, accidents can still happen. Throughout DrM’s long involvement in the design and installation of filtration systems of hazardous products, it has encountered a number of incidents that merit mentioning.  Exposure to and knowledge of these incidents have allowed DrM to develop safe designs fig2

Material Handling Risk

The risk of industrial accidents involving liquid handling is generally very low as liquids can easily be conveyed in pipes and processed in closed equipment. Explosion-proof components such as pumps, agitators, valves and instruments are generally considered to be reliable and safe.

On the other hand, solids handling is another matter. Material blocking, accumulation, sticking and dust creation are just a few solids handling issues that can pose safety fig3problems. Furthermore, the behaviour of a solid/liquid mix can significantly change as a result of varying concentrations. This can create unexpected and undesirable results.

Filter systems for solid/liquid separation are at intersection of liquid and solid handling.  Since the FUNDABAC® filter is often used to generate dry solids from a liquid stream, appropriate designs are required to handle those powdered solids. As long as the solids are contained in the enclosed filter, safety can be guaranteed. Once the solids are discharged, containment becomes significantly more challenging. Here are some typical issues that DrM has encountered.

Inert gas for cake drying
Unfortunately it still happens that inert gas gets contaminated with air. Depending on temperature, solids and liquid composition as well as dryness of the product the consequences are manifold.  In most of the cases we experienced, the pyrophoric cake, such as catalyst starts to glow and slowly burns. Luckily, oxygen levels are often low which may only cause some material damage. However, the consequences can be significantly more devastating and it is recommended to constantly monitor the inert gas quality.
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Steam For Cake Drying
Some DrM clients prefer to use steam to dry the cake of solids. To prevent moist discharge, superheated steam can be used (please contact DrM for further information).

The use of superheated steam results in a hot cake of solids that could create issues during discharge that are not normally encountered with cake drying using inert gas. For example, while a cake may be handled safely at ambient conditions, it may become significantly more pyrophoric at elevated temperatures. To prevent any incidents, it is recommended to cool the cake by inert gas purging prior to discharge. As an alternative, saturated steam or water spray can be applied to keep the cake humid.

Solids Containment and Handling

Operators may decide that complete containment of the cake is required. This is easier said than done. If the solids are processed indoors, closed equipment can be installed on the discharge side of the filter.

Containers may be closed with a manual valve and transported to the next operation unit. Alternatively, the cake can be transformed into pulp for easier handling.fig5
When solids need to be shipped to another facility or disposed of, one way containers or barrels are preferred. These need to be positioned onto the discharge chute of the filter. If the discharge operation needs to be contained, an endless bag may be an option.

When solids are hot,  polyethylene bags may not be an option. An alternative would be to let the cake cool off in the filter by way of inert gas purging and discharged when the temperature falls below 60ºC. A flexible bellow, designed for manual or pneumatic operation, can be pressed onto a steel barrel.