Intelligent, Efficient Plant Control

Both Ex and non-Ex areas can be found in wastewater plants. The WAGO-I/O-SYSTEM 750 allows efficient plant control for both areas.

Several specialized and general regulations complicate the construction and operation of a wastewater plant, making it anything but easy. Planners and operators can significantly lower their expenditures by selecting an intelligent control system that supports standard and special applications equally.

One thing is for certain: It is almost impossible to predict the composition of the effluents arriving in wastewater plants. Contaminations, flammable compositions or chemical reactions can occur at any time due to accidents or unauthorized discharges. These may result in outgassing, which must be classified as a hazardous atmosphere. If highly flammable liquids, such as gasoline, get into the sewer system, they will float on the surface due to their lower density. As volatile materials, they evaporate quickly; depending on their concentration, they can create a harmful or even explosive mixture. Since the vapors that are generated are often heavier than air, they inevitably collect at the lowest point of the sewer network. Therefore, the sewer network and its structures, such as enclosed storage basins for wastewater, stowage canals, pumps or inverted siphon structures, are classified as Zone 1 or Zone 2 depending on their design.

A very high concentration of sludge gases is actually related to the function of the rake structure, because coarse and fine materials, such as tree branches, textiles and hygienic items, are separated here. Accordingly, this area is classified in the hazard assessment as Zone 1 and adjacent areas as Zone 2. This classification also applies to sludge water reservoirs, such as shafts and structures, of the de-sludging step. The anaerobic bacterial processes, active during sludge decomposition in the wastewater, are used in the digester tower of the sewage treatment plant to extract sludge gases. These sludge gases will be converted into electricity and heat in a downstream block heat and power plant to positively impact the wastewater treatment plant’s energy balance. The process areas, from sludge thickening up to sludge decomposition, are also classified as Zone 1 and Zone 2 as part of the hazard assessment; The same applies to the outer areas of the sludge and gas container.

Both the planner and operator are usually interested in minimizing the number of components and systems that must be used. For good reason: The complex requirements the waste water plant places on the control system impact the foreseeable expenditures for planners and operators, from initial engineering to eventual maintenance. Accordingly, they prefer products that can be used in both standard applications and hazardous applications, such as the highly aggressive or corrosive environments typically found in sewage treatment plants.

WAGO’s modular components enable planners to equip applications in the Ex and non-Ex areas economically and efficiently without extensive programming. Operators can also implement special solutions, such as partial energy measurement and storage of all process data, with the components of an automation system. This makes it possible to establish a targeted monitoring and management system that will display historic values. WAGO’s I/O system also provides function libraries for water and process systems free of charge, benefiting both the process engineer and programmer.

Author: Kay Miller