Screen cleaning
There are many types of screen used in the water industry.
Combined Sewer Overflows (CSOs) are a crucial component of a combined sewer system. In these systems, rainwater mixes with wastewater, which can lead to excessive water volumes during heavy rainfall. Without suitable measures, the system may discharge excess water through overflow points. Screens are installed in CSO chambers to remove solids from the overflowing water, keeping them in the sewer system and reducing pollution. Over time, these screens can become blocked or clogged, however, and therefore require regular cleaning to remain effective.
The details below focus on CSO screens as this is a useful way to highlight the features of our screen cleaning systems. But the products detailed below can be used to clean many other types of screens in the water industry.
CSO Screens
CSO chambers allow the water level to rise naturally in times of heavy rain and then diver into an overflow pipe. The excess water is then piped away to either be stored in attenuation tanks or to be discharged at predefined points into the sea or waterways. The CSO system, therefore, prevents sewage water from discharging where it is not wanted, for example in the street!
A vital part of a CSO chamber is the screening system. This removes solids from the overflow water and keeps them within the sewage system rather than the overflow system. This prevents solid waste from being discharged into waterways. In effect, the screens keep the worst of waste within the sewage system proper.
There are many designs of screens deployed in CSO systems. Often, the screens deployed will require regular cleaning to keep them free from debris. If debris builds up over time, the screen will not allow enough water to pass through it, and thus it becomes less effective. As such, clogged screens can become a serious problem for water companies. If the problem gets too bad it can result in uncontrolled discharges of raw sewage.
Wave screens
A common type of static screen used in CSO systems is the waveform screen. The wave form of a screen increases its surface area and so increases its ability to effectively filter solids from large volumes of water. However, the wave nature of the screen also increases the opportunity for solids to become lodged within the screen during operation. Furthermore, when washing down from the top, the structure of the screen will act to block any cleaning jets used and so inhibit effective cleaning.
The solution
To overcome this, we have developed specific screen cleaning systems. The ScreenBlaster is an 8-nozzle rotary jet cleaner. This is a variant of models commonly used in tank cleaning applications.
The system is entirely fluid-powered. Wash water is pumped through the cleaning head at between 8 and 10 bar pressure. This drives a turbine when rotates the cleaning head in two orientations. The wash fluid then passes through 8 cleaning jet nozzles. The result of this is that 8 powerful jets of water are indexed around the target surface such that they are brought to bare on the entire surface over a set cleaning cycle time. This mimics the effect of someone manually cleaning the surfaces with a high-pressure hose.
Normally, tank cleaning heads of this nature will bring their cleaning jets to work a complete 360° clean. The 8 Nozzle design of ScreenBlaster, however, allows for the cleaning pattern to be restricted to as small as 90°. What this means is that the powerful cleaning jets will impact each part of the surface below with a 90° (or more) cone.
To overcome the natural blocking of the cleaning jets by the wave nature of the screen we design such systems so that as much of the screen is within a 60° cone of the ScreenBlaster. This helps reduce the effects of shadowing. The cleaning jets that impact the screen between the 60° and 90° cone still produce some cleaning and so are still effective but with the 60°, narrower cone, we get excellent cleaning of the screen. These simple design parameters ensure screens are kept fully operational.