Steam generation with 2-in-1 relay modules

Phoenix Contact Pty Ltd

Tuesday, 20 August, 2013


Steam generation with 2-in-1 relay modules

The production of agricultural and industrial chemicals frequently involves the use of steam-powered plants, and pure water is needed to generate the steam for such plants. SKW Stickstoffwerke Piesteritz uses Phoenix Contact coupling relays to control their generators as they require less space in the control cabinet.

SKW Stickstoffwerke Piesteritz - with 800 employees and based in Wittenberg - is Germany’s largest ammonia and urea nitrate producer. Every year, the company produces in excess of three million metric tons of basic materials for the industrial and agricultural chemicals sector. The company’s products and services also include agricultural products that help farmers secure yields that are both profitable and environmentally friendly. As well as the production of chemicals, this involves a lot of research. The in-house research and development department has 62 employees, and more than 100 patents have been registered to date.

The SKW Stickstoffwerke Piesteritz in-house water treatment plant is used to purify water for steam generation. This entails several processing steps. First, untreated water is piped in from the nearby Elbe River. The river water is passed through a coarse filter that removes the roughest dirt. This prefiltered water, known as raw water, is then fine filtered and softened. Softening involves the freed-up calcium being removed from the raw water, which would otherwise cause unwanted lime scale in the pipes. This step is similar to adding a decalcifier to the wash cycle in a domestic dishwasher. The product from this is so-called ‘soft’ water.

The soft water is then further purified through either distillation or demineralisation. With demineralisation, the freed-up ions from one substance in the water are replaced with identically charged ions of another substance. For this, the soft water is fed through an ion exchanger. Here, the ions to be replaced are bound to the ion exchanger, which simultaneously releases the replacement ions into the water. Distillation, on the other hand, uses evaporation and condensation to remove the unwanted elements from the soft water. The first step of this is to raise the water temperature to boiling point. The resulting steam is fed through a condenser, which turns it back into liquid form. This is usually done in several steps in order to achieve the required purity level. As a last step, the distilled/demineralised water is desalinated, which turns it into fully deionised water. Again, ion exchangers are used for this. The deionised water is then employed to generate the steam required for powering the plant.

Steam can be used in many different ways. For one, it is used to drive the turbines in the chemicals section of the factory. The turbines power the pumps, compressors and fans in the ammonia and urea nitrate production plant. Steam is also deployed in processing, directly. For example, it is used for the reforming of natural gas, whereby the gas is split into different gas fractions. These fractions are then used as basic chemicals for urea nitrate production. Lastly, SKW Stickstoffwerke Piesteritz uses steam for heating.

As part of the water-treatment system, actuator assemblies driven by solenoid valves are used to control the process substances.

“We have grouped the solenoid valves into valve units,” explains Norbert Reuter, an automation technician at SKW Stickstoffwerke Piesteritz’s Engineering Technology Department. “These valve units are controlled by a block of Phoenix Contact PLC-2RSC-24DC/1 relay modules. Each relay module is assigned to a separate solenoid valve.”

The relay module has two functions: firstly, one of the integrated relays controls the solenoid valve. For this, the electrical ‘on’ and ‘off’ signals are converted into pneumatic ‘air on’ and ‘air off’ signals. The pneumatic control opens and closes the valve. The second integrated relay is used to receive status messages about the valve’s operation.

Through the use of PLC-2RSC-24DC/1 relay modules, both of these functions - ‘control’ and ‘status messaging’ - can be implemented within a single compact unit.

The PLC-2RSC-24DC/1 relay modules feature two integrated relays and can be installed in compact spaces.

The PLC-2RSC-24DC/1 relay modules feature two integrated relays and can be installed in compact spaces.

“This is the main reason why we picked the Phoenix Contact component,” explains Reuter. “Our new switchgear room for controlling the water treatment needed to be housed in an existing building with limited space. Also, we liked the well-laid-out wiring of the modules.”

Wiring transparency is granted through the use of bridge plugs for distributing the current. These are plugged into the PLC module in order to distribute the shared voltages directly. The length of the bridge plugs can be trimmed individually, which means that up to 80 modules can be supplied with the same voltage.

Some of the other controller applications also make use of Phoenix Contact relays, such as the PLC-RSC 24DC/21-21 AU and the PLC-RSC 24DC/21-21. Among others, these are used to couple and decouple signals that control electrical drives.

Using PLC-2RSC-24DC/1 relay modules with two integrated relays provides twice as many channels than conventional 6.2 mm components. Phoenix Contact thus offers a very convenient solution for applications that have restricted installation space. As well as the screw-type connection technology chosen by SKW Stickstoffwerke Piesteritz, the relay modules are available with spring-cage or push-in connections.


Photograph: SKW Stickstoffwerke Piesteritz GmbH

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