Treatment methods for flue gas of boilers and production wastewater

According to technological design, most of wastewater from production process is recycling to production line. However, factually some small quantity of wastewater is discharged to surrounding environment.

The measurement shows that pH of wastewater is about 12, exceeding the discharge standard to receiving resources. Most factories directly discharge it to outside without any treatment. Some others, including Dong Anh cement roofing tile enterprise, scour boiler gases to basin of wastewater to neutralize it primarily. Then wastewater is manually neutralized by acid. This system has been stopped operating due to uncontrolled acid supply leading to excessive acid consumption.

In frame of Project “Mitigation measures in Building materials industry” of Ministry of Construction supported by DANIDA in 2003, National Institute of Labor Protection carried out the design consultancy, manufacturing and evaluation of two air and wastewater treatment systems in He Duong roofing sheet production enterprise.

In frame of Project “Mitigation measures in Building materials industry” of Ministry of Construction supported by DANIDA in 2003, National Institute of Labor Protection carried out the design consultancy, manufacturing and evaluation of two air and wastewater treatment systems in He Duong roofing sheet production enterprise. The task is to select a technical solution so that gases and wastewater are well exchanging matter each to other and neutralization process is most effective. The designers had select Packed Tower as a device where the matter exchange process between boiler gases and wastewater is carried out. Ceramic rings, ordered from Bat Trang Ceramic Village, are used.

Operation principles

Wastewater is running to the receiving basin by open canal. This basin contains and regulates wastewater flow. Wastewater is pumped to Packed Tower and steadily distributed to packed layer through a system of lotus taps, then moving downwards through the packed layer. Boiler gases are moving upwards through the packed layer against the direction of wastewater movement.

Matter exchange process between boiler gases and wastewater happens on the internal surfaces of the packed layer. Dust and dissolved SO2 are moving downwards to neutralization basin, while cleaned gases are released to atmosphere. The neutralization process is continuing in neutralization basin. A clear opening at bottom connects neutralization and sedimentation basins each to other. At sedimentation basin dust and precipitates are settled on bottom, wile water is discharged to river or returned to receiving basin depending on pH measured.

Treatment facility for flue gas of boilers and production wastewater in He Duong Roofing Tile enterprise
Treatment facility for flue gas of boilers and production wastewater
in He Duong Roofing Tile enterprise

As wastewater flow (0,5 m3/h) to be treated is less than flow supplied to Packed Tower (1-1,5 m3/h), recycling of treated wastewater from sedimentation basin to receiving basin could be organized for continuing neutralization process in case of pH still higher than allowed discharge standard. In case of pH meeting the discharge standard treated wastewater is directly discharged to river or recycled to clean water tower. Clean water supply system has 2 functions: 1) Water supplement to Packed Tower in case of insufficient of wastewater; 2) water supply for cleaning Packed Tower before stopping operation.

System scheme
system-scheme

P1- Fan
P2- Recycling and Basin drying Pump
P3- Supplying Pump
V1- Valve supplying water to Packed Tower
V2- Valve recycling water for cleaning Packed Tower
V3- Valve exhausting wastewater for P3
V4- Valve exhausting clean water for P3
V5- Valve supplying clean water
V6- Valve supplying clean water for reducing temperature of water in sedimentation basin
V7- Valve recycling treated wastewater from sedimentation basin to receiving basin
V8- Valve discharging treated wastewater to river
V9- Valve discharging wastewater from neutralization-sedimentation basin for drying it.
V10- Valve recycling treated wastewater to clean tower

Trinh Huong


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