Application of fully automatic filters in wastewater treatment and reclaimed water reuse in ammonium phosphate plants

Application of fully automatic filters in wastewater treatment and reclaimed water reuse in ammonium phosphate plants

1.1 Sulfuric acid workshop

The sulfuric acid workshop uses mixed ore as the production raw material, the purification section adopts an electric dust removal closed acid washing process, and the absorption section adopts a two to two absorption acid production process. The wastewater discharged from the workshop mainly includes dilute acid wastewater, drum cooling water, and circulating water.

The dilute acid wastewater mainly comes from the purification section. During normal production, the dilute acid sludge is discharged twice a day. In addition, there is a small amount of acid leakage from the concentrated sulfuric acid cast iron pipe cooler in the dry suction section, and a small amount of acid and alkali wastewater is discharged from the desalination station.

Drum cooling water is used to cool the slag discharge drum, which contains a large amount of suspended solids due to the mixing of a large amount of pyrite slag.
1.2 Phosphate fertilizer workshop

The phosphate fertilizer workshop uses phosphate ore as raw material and produces phosphate fertilizer through processes such as crushing, ball milling, mixing, and maturation. The fluorine containing tail gas in the mixing process is absorbed by a two-stage absorption chamber. The wastewater from the synthesis tank and centrifuge of Sodium fluorosilicate synthesis process is acidic fluoride containing wastewater, mainly containing Sodium fluorosilicate and hydrochloric acid.

1.3 Ammonium phosphate workshop

The ammonium phosphate workshop consists of two sections: phosphoric acid and ammonium phosphate. The phosphoric acid section uses the slurry produced by the phosphate fertilizer workshop and sulfuric acid produced by the sulfuric acid workshop as raw materials, and produces phosphoric acid through processes such as leather extraction and filtration.

The ammonium phosphate section uses nitrogen and phosphoric acid as raw materials and produces ammonium phosphate through processes such as neutralization, concentration, granulation, and drying. The cooling water for various equipment in this section is about 40m3/h, which is directly discharged without recycling; The condensate discharged from the mixed condenser is mainly used. During normal production, the pH, phosphate, fluoride, and suspended solids of this wastewater can all meet the standards, but when the operation is unstable.

2. Wastewater treatment and reuse

Wastewater can be divided into two categories, namely cooling water and acidic wastewater or acidic fluorinated wastewater. The former has a large amount of water and slight pollution, but it directly wastes a large amount of fresh water. Therefore, measures should be taken to improve the circulating cooling water system as the main control measure; The latter has a small amount of water but severe pollution, and appropriate treatment measures should be taken before being reused for production or discharged to meet standards.

2.1 Cooling water

2.1.1 Cooling water for sulfuric acid workshop drum

The drainage of the circulating cooling water system is directly discharged after the cooling drum. Now there is a water collection device installed below the drum and it is piped to a clean water tank, which is then reused for cooling the drum.

2.1.2 Circulating cooling water for sulfuric acid workshop

The original circulating cooling water system had poor cooling effect due to reasons such as the collapse of the cooling tower packing.

2.2 Acid wastewater and acidic fluorinated wastewater

2.2.1 Acid wastewater from sulfuric acid workshop

Due to its low arsenic content, the standard can be achieved by using a general lime method for one treatment. The workshop originally had a set of dilute acid wastewater treatment facilities, and after renovation, the wastewater can meet the discharge standards.

2.2.2 Acid fluorinated wastewater from phosphate fertilizer workshop

The acidic fluorinated wastewater in the workshop adopts a two-stage lime neutralization and sedimentation process. When the workshop production is normal, the wastewater is neutralized with lime milk once to pH=5-6. After solid-liquid separation, the supernatant is reused for grinding; When the workshop production is abnormal and the system water balance is not balanced, the wastewater treatment operates in a two-stage lime neutralization and sedimentation method, and the wastewater can be discharged up to standard.

During the operation of the workshop wastewater treatment device, there are problems such as high lime consumption and low processing capacity of the ash machine and frame filter press. At present, the wastewater is mixed with mineral powder and directly reused for grinding. After more than five months of operation, it has not affected the grinding system equipment. This can reduce operating costs and achieve closed circulation of wastewater.

2.2.3 Acid fluorinated wastewater from ammonium phosphate workshop

The original plan was to incorporate the extraction tail gas washing water into the wastewater treatment system of the phosphate fertilizer production workshop for treatment, but its water volume exceeded the needs of the grinding process. Therefore, the extraction tail gas washing water was used as the secondary washing water for the disc filter in the filtration process.