Evaporation crystallization process of ammonium sulfate wastewater

Evaporation crystallization process of ammonium sulfate wastewater

Ammonium sulfate wastewater is easy to be produced in fermentation, waste gas absorption and industrial production industries. Generally, the water volume is large and the content of ammonium sulfate is high (≥ 10%). The front end is not suitable for reduction treatment by membrane concentration or electrodialysis. The wastewater directly enters the evaporation system, and the produced water is reused / biochemical. Crystalline salt is used as by-product ammonium sulfate (fertilizer).

1、 Project Overview:

1. Material name: ammonium sulfate solution.

2.Feed parameters: ammonium sulfate concentration: 10%, temperature: normal temperature (0 ~ 40 ℃), feed volume: 12t / h, pH value: 4 ~ 5, hardness < 200mg / L.

3.Discharge parameters: crystal discharge, discharge volume: 1.2t/h.

4.Design evaporation capacity: 10.8t/h.

5.Configure the packaging device.

6.Equipment material: 2205 is used for the part in contact with materials, and 316L is used for other parts.

7.Control mode: PLC control.

8.Material source: dilute sulfuric acid is used to adsorb ammonia to form ammonium sulfate solution, and the pH is adjusted by adding ammonium carbonate to neutralize sulfuric acid. The source of impurities in the material is the process water used to prepare dilute acid. The purity of ammonium sulfate can be guaranteed if the evaporated condensate is returned to the acid preparation unit.

Boiling point temperature rise of ammonium sulfate:

图片1 1

Ammonium sulfate solubility:

图片2 1

Main process flow:


2、 Process Overview:

1) Feed tank → feed pump → preheater → forced circulation heat exchanger → crystallizer (steam → compressor → heat exchanger) → discharge pump → salt slurry

2) The raw liquid is first heat exchanged by the feed pump through the condensate heat exchanger, and then enters the non condensable preheater for further heat exchange and temperature rise. The heat source is distilled water produced by evaporation and non condensable steam discharged from the system.

3) The preheated material liquid enters into the forced circulation evaporator, where it is evaporated, concentrated and crystallized until crystal salt appears in the solution, and then the salt slurry is transported by the discharge pump for discharging.

 4) The secondary steam generated by the separator enters the compressor for compression, and the high-temperature steam compressed by the compressor enters the forced circulation heater. The steam in the shell side of the forced circulation heater is condensed into condensed water, which is discharged into the condensed water tank and pumped into the condensed water heat exchanger through the condensate pump to preheat the material.

5) The non condensable gas in the shell side of the forced circulation evaporator enters the non condensable gas heat exchanger to further preheat the materials.

6) Each compressor of the system is separately equipped with a liquid accumulation tank and a drain pump, and the condensate in the liquid accumulation tank is transferred to the condensate tank through the drain pump.

7) The heater is divided into two parts and connected in series in front of and behind the axial-flow pump, which reduces the circulation capacity of the circulation pump while meeting the flow rate between the material pipes, which is conducive to the cultivation and growth of crystals.

8) Ammonium sulfate is characterized by its high solubility, easy scarring, scaling and blocking of equipment and pipes, hard solid after blocking, and difficult cleaning, which cause a lot of inconvenience to the evaporation crystallization process. Therefore, in the design of the MVR evaporative crystallization system of ammonium sulfate, it is necessary to pay attention to the blocking problem of ammonium sulfate crystals, and to consider anti blocking measures such as purging and replacement in the liquid level measurement positions, discharge ports, pipes, pumps, etc. of the equipment.

3、 Process characteristics:

1.High salt content, horizontal piston double push centrifuge, automatic discharge, greatly reducing labor intensity and saving labor.

2.The heat exchange tube of MVR heater is 2205, the tube sheet is 2205, the shell side is 316L, and the MVR separator is 316L; 316L circulating pipe and 316L discharge pipe are used; 316L secondary steam pipeline is selected; 316L shall be selected for pipes and vessels in contact with condensed water.

3.Centrifugal high temperature rise steam compressor is adopted, with spiral case of 316L, impeller of TC4 and temperature rise of 18 ℃.

4.The circulation pump adopts a large flow and low lift axial flow pump to reduce motor power consumption and save operating costs.

5.MVR evaporative crystallizer system adopts forced circulation, which is stable and saves energy consumption.

6.The crystallizer adopts OSLO, which can greatly eliminate the supersaturation of ammonium sulfate solution and is conducive to crystal growth. The system is designed for negative pressure evaporation to reduce the evaporation temperature as much as possible.

7.To prevent liquid from being entrained in the steam due to evaporation in the evaporator, a defoaming device is arranged at the upper part of the evaporator; Adding defoamer dosing device further reduces the generation of foam during evaporation.

8.A conductivity meter is installed on the outlet pipe of distilled water to detect the conductivity of distilled water online, control the flow direction of distilled water through the outlet control valve, reuse qualified distilled water, and continue to treat unqualified distilled water in the evaporation raw water tank.

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