Trial Washing Plant – Technical Details
The Parnaby washing plant is best visualised as two smaller circuits working together to form the overall system.
- The top system is the washing/separation section of the plant, which is running continuously.
- The bottom system is the water treatment section of the plant, which is also running continuously.
- Dirty water leaves the washing/separation circuit to be processed by the water treatment circuit.
- ‘Clarified’ or recycled, cleaned water then is re-introduced back to the washing/separation circuit.
From first turning on the washing plant, this continuous full closed loop system is cleaning its water automatically at a rate of approx. 120m3/hr.
Visual Process Description
The raw feed material is fed into the reception hopper where there is basic size protection (static grid). From here it is conveyed directly into the Parnaby 7/30 barrel separator. The material is flushed down the feed launder and into the barrel. As the water cascades down the barrel, passing over the internally welded scroll section, the lower density materials such as paper, organics and plastics floats down this river effect, to the floats product dewatering section. The heavier denser glass, and ceramic sink, and are scrolled up to the top of the barrel. This is a process of separation by density, and also dynamic effect. By this we mean we can control a number of parameters within the barrel system such as:
1. Barrel speed.
2. Velocity of flushing water down the barrel.
This therefore allows us to actually ‘set’ the separation cut point between materials. For example, by increasing the velocity of the water down the barrel we can separate
‘near density’ materials such as high density plastics from the glass unlike most other dry processes.
As the lower density material is flushed down the barrel, cascading over the internal scrolls, it is initially de-watered by the barrel Trommel screen.
This screen is bolted to the end of the barrel separator and is driven by the same drive arrangement. The Trommel screen is typically set at 1mm aperture and comes complete with stainless steel wedge wire panels. This Trommel is also self-cleaning with fully automated, self-cleaning spray bars. The spray bars themselves have actuators, which drive a brush up inside the manifold to keep the spray nozzle heads clean. The solids removed from the spray bars are flushed down into the collection tank below.
As the material exits the barrel Trommel, it goes onto further de-watering via an inclined vibratory screen. This screen is inclined to increase residency time for aided
de-watering. Again we use stainless steel wedge wire panels of 1mm aperture.
The liquid collection tank below or ‘balance tank’, recirculates this liquid back up to the barrel feed launder as a continuous process to receive and flush in new material.
The effluent bleed point is also located on this tank, constantly with a controlled overflow to send the dirty wash water to the effluent treatment section of the plant.
At the top end of the barrel, all heavy, dense material such as the glass and ceramics have sunk and been scrolled up by the internal welded scrolling within the barrel. This material is then discharged onto the glass washing and rinsing screen as shown here on the left. The material is rinsed with a series of spray bars to wet screen through the various product size fractions required.
This rinsing also helps liberate any final organics or contamination, this glass is then pumped to both primary and secondary Parnaby Hydro Cyclone separators for separation from the residual paper and plastic. As per the Parnaby Barrel Separator, dynamic effect, plus the natural difference in density, efficiently cleans and removes the contamination.
Any paper and plastic recovered by the cyclones is consolidated with the paper and plastic initially removed by the barrel separator to produce a common discharge point of these materials from the plant.
The first part of the water treatment section of the system is the Parnaby Water Cleaning Cyclones. As the diagram shows the coarse paper particles <100um – 1mm are recovered and extracted prior to further treatment of the cyclone overflow in the DAF (Dissolved air floatation) system. The Parnaby Water Cleaning Cyclones again use dynamic effect to separate material this time on size not density. The solids are removed from the water to help take solids loading away from the rest of the water treatment equipment.
The Parnaby DAF system is a combination of both mechanical and chemical processes, where the chemical (flocculent) is used to pull together solids (+ charge)to the chemical which is negatively charged. This means very small particles of paper fibre are consolidated into larger solids. As the solids collect they float to the surface for removal. To aid in the floating of organics, the vessel is introduced with a curtain of micro-bubbles. These solids are then removed with a mechanical skimmer located on the top of the DAF, sending the solids to the buffer tank before final pressing through the Parnaby Belt Press.
Solids from both the top and bottom of the Thickener DAF system are delivered to the buffer tank. Here the buffer tank stirrer is used to ensure a homogenised state of the sludge before pressing. As with all processes a more consistent feed material ensures more consistent operation and de-watering capability of the filter belt press.
The sludge is pumped from the buffer tank to the reception hopper positioned over top of the filter belt press. Here a paddle within the reception hopper distributes the sludge evenly over the width of the belt.
Additional flocculent chemical can be added at this stage to aid in the de-watering of the sludge.
between the two belts over and under a series of compression rollers to push out the remaining moisture.
The filter cake is removed at the opposite end of the machine, with a scraper to clean the belt. Additional cleaning of both top and bottom belts is facilitated with two self-cleaning spray bar systems, one dedicated to top belt cleaning, the second dedicated to the cleaning of the bottom belt. This cleaning of belts is a continuous process when the machine is running, so the belt is always cleaned before receiving the next load of sludge.
Moisture from the belt press is collected in a steel collection tank and is pumped back to the thickener DAF system, and therefore kept in circuit, cleaned and re-used as spray water back on the washing plant section of the process, and for the belt membrane cleaning as mentioned above.
Mechanical filters are used around the plant on important recycled wash water lines, to protect spray nozzles from blocking. These filters act as another form of protection, and come complete with pressure transducers. If the filters become blocked and the spray pressure drops, a warning is issued on the touch screen of the PLC. For example – “Warning low pressure, check filter no.1″
Every mechanical filter comes complete with an inline filter and a separate ‘stand by’ filter which can be used to ensure continuous running of the plant.
As with all Parnaby Washing Plant, we understand the responsibility of the plant operators, and therefore we take pride in our operator training.
However to help remove some of the responsibilities and make the system as easy to monitor and operate as possible, all Parnaby Washing Plant come with a range of automation features:
1. Ultrasonic and DP Cells for liquid level indication and control.
2. Pressure transducers for pressure indication and control, for example on spray bars around the plant.
3. Solids Sensor for measuring solids % within the clarified (recycled) wash water, which automates chemical dosing as part of the mechanical and chemical process of water cleaning.
4. Liquid volume indication, via mag flow gauges, for monitoring of the liquid flows between the washing / separation and water treatment sections of the plant.