Rotary drum grille is the ideal wastewater treatment equipment in the pretreatment of sewage treatment. It is widely used to intercept and remove the grille slag in sewage to ensure the normal operation of mechanical equipment, process instruments and subsequent biochemical treatment. Therefore, Rotary drum grille plays a key role in the pretreatment process of sewage treatment.
A wastewater treatment plant in Zhucheng, Shandong, has a wastewater processing capacity of 2000 m3/h. The biochemical treatment unit adopts the improved A2/O process, with two rotary drum grilles. The effect of rotary drum grille interception and slag removal is not unsatisfactory.
After the overhaul and replacement of rake teeth in 2014, the performance of rotary drum grille has improved slightly, but there are still a lot of problems: Garbage is often blocked at the valve port of sampling pump of intake detection instrument, which affects sampling pump; Garbage is wrapped around the probes of DO, MLSS and ORP in biochemical pond process instrument, which can not accurately detect real-time data; there are a large number of poultry hair and garbage floating on the surface of biochemical pond, especially in anoxic pond, which seriously affects the sense; The scraper of sludge concentrator and dewaterer has a large amount of fibrous garbage accumulation, which leads to unclean scraping and so on. Now rotary drum grille can not meet the production needs at all. Zhucheng sewage treatment plant seeks suitable transformation scheme to solve the above problems, so as to make the effluent meet the requirements of relevant standards.
Runneng sewage treatment engineers arrived at the site, then studied and analyzed the operation of rotary drum grille, grille overhaul or replacement, according to the biochemical process and production process problems.
Retrofit scheme of rotary drum grille
The operational life of rotary drum grille is long and the overall operation efficiency of the equipment is low. According to the actual operation of the grille, the environmental protection engineers of Runneng listed the following specific modifications:
(1)Because of the serious wear and tear of the transmission shaft, the transmission system of rotary drum grille is replaced to solve the problem of unsmoothly operation.
(2) In view of the replacement of nylon rake teeth in 2014 and the fracture of some rake teeth after four years of operation, it is now decided to replace all rake teeth with stainless steel rake teeth, so as to avoid the fracture of rake teeth during operation, resulting in the unable removal of small grid slag;
(3) The overall reduction of rotary drum grille rack makes the bottom of the equipment contact with the floor of civil concrete, and completely intercepts the fine grille slag.
(4)Replacing the brush with the steel brush can delay fibre winding. And regularly increasing the manual cleaning force can extend the service life of steel brushes.
(5) After replacing stainless steel rake teeth of rotary drum grille, grille spacing should be strictly controlled to 5 mm to ensure the effect of intercepting and removing grille slag.
(6) Aiming at the problems of large quantities of chicken feathers and duck feathers on holidays, we cooperate with manual salvage after overhaul of rotary drum grille.
After reforming the above parts of the grille, it can solve the current problems and ensure the normal operation of the production process. But the cost of transformation is huge, which is comparable to replacing a new rotary drum grille.
Replacement scheme of fine grille equipment
According to the installation location, size and civil engineering data of existing grille in Zhucheng sewage treatment plant, rotary drum grille and vertical orifice grille machine are selected for comparative analysis. The comparative analysis table is as follows:
|Name||Classification||Structure and working principle||Advantage||shortcoming|
|Rotary drum grille||Outward rotation type||Rotary drum grille is installed in the entering trench at a 35 degree angle with the horizontal plane. Sewage flows into the drum from the end of the rotaty drum. Water flows out through the grille gap on the side of the drum. The grille machine is installed in the entering trench at a 35 degree angle with the horizontal plane. Sewage flows into the drum from the end of the rotaty drum. Water flows out through the grille gap on the side of the drum. The grille keeps the floating substances in the water in the turning stock. The drum rotates at a certain speed. Above the drum are nylon brushes and flushing water nozzles, which can remove the grate slag and run through screw conveyor to squeeze dry, dehydrate and transport to the upper hopper, which can be transported by conveyor.||A 35 degree angle is formed between the grille and the flow, and the baffle can be formed, even if the thickness is less than the gap of the grille, the fine floating matter can be separated. The grille is equipped with a flushing device and has self-cleaning function; Cylindrical structure has larger flow rate and smaller head loss than traditional grid; Moreover, the accumulation plane in front of the grille decreases; The integrated interception, transportation and pressing treatment of the grille not only saves the area occupied, but also reduces the cost of subsequent treatment of garbag; Less maintenance||When the drum rotates to the top, part of the grid slag can not fall into the central conveyor trough under the action of nylon brush and high-pressure flushing water. The gap between the grid slag is blocked, resulting in increased head loss.|
|Internal rotation type||Rotary drum grille is installed in the intake channel at a 35 angle with the horizontal plane, sewage flows from the open port of the grid into the channel through the grid, which intercepts the solid floats. When a certain water level difference is reached, the rotating rake positioned on the central axis rotates in the grate drum. The rotating rake teeth are inserted into the grate to clean the grate and drive upward operation. When the rotary rake teeth run to the highest point, all the grid slag falls into the central grid slag spiral groove, and through the central grid slag spiral groove screw conveyor press to dry, dehydrate, and transport to the upper discharging hopper discharge.||Rotary drum grille runs well and can effectively remove fibrous grating slag from sewage.|
|Vertical orifice thin grille||Vertical orifice thin grille||Vertical orifice grille is mainly composed of main frame, rotating net and chain, driving unit, slag collecting trough, backwashing system and control system. Sewage enters from the middle of one side of the vertical orifice grille and discharges from the inside to the outside through the two sides of the orifice grille. The slag intercepted in the inner part is lifted to the upper slag discharging area along with the rotation of the perforated grid plate. The grate slag is washed by the flushing system into the inner slag collecting trough, and then through the conveyor into the screw conveyor, while the mesh plate is also flushed clean and into the next working cycle.||The mesh plate has large water intake area and high slag retention rate; Vertical installation, effectively saving space; Eliminate the problem of filament and hair winding; The screen plate has the advantages of low friction, wear resistance, non-blocking and easy cleaning.||Pervious holes are round holes, and a large amount of floating matter is easily attached to them, resulting in accumulation of water intake and increased head loss.|
Based on the performance and economic comparison of the above grille filters, and the operation experience of the same sewage plant, the conclusion is drawn:
- The cost of maintenance and transformation of the original rotary drum grille is too high and uneconomical, and the ability of the grille to intercept small floating matter is insufficient;
- Vertical orifice thin grids are easy to cause inflow accumulation and head loss;
- Rotary drum grille runs well and can effectively remove fibrous grille slag from sewage;
After many discussions by the professional sewage treatment engineer of Runneng, it was finally decided to replace the existing rotary drum grille.
Technical parameters of rotary drum grille
Model is RN-ZGGS-1200
Water treatment capacity is 1110 m3/h
Grille material is stainless steel
Grille grid gap is 5mm
Drum diameter is 1200mm
Motor power is 1.5 kW
Installation angle is 35 degrees
Quantity is 2 sets
In 2018, two RN-ZGGS-1200 rotary drum grilles were delivered to Zhucheng sewage treatment plant in Shandong Province by Runneng. After installation of the grille, technicians carried out commissioning and trial operation. After a period of rotary drum grille operation, the problems existed in the production process have been significantly improved, and a series of indicators in the effluent, such as CODCr < 50mg/L, BOD5 < 10mg/L, SS < 20mg/L, NH3-N < 5mg/L, all meet the requirements of DB37/599-2006, Comprehensive Discharge Standard of Water Pollutants along South-to-North Water Transfer in Shandong Province. The transformation project of rotary drum grille in a sewage treatment plant in Zhucheng, Shandong Province meets the production needs of this wastewater treatment plant.
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