Conversion of thermal deaerator to vacuum deaerator

1、 Working principle:

The operation of a thermal deaerator requires steam to heat the feedwater to saturation, reducing the surface tension difference of water to discharge oxygen and other gases, which consumes a considerable amount of heat. Steam in cogeneration projects is more economical compared to electricity generation.

The working principle of vacuum deoxygenation is to apply Henry's law and Dalton's law. According to Henry's law, in a closed container, if any gas exists on the water surface at the same time, the solubility of the gas is proportional to its own partial pressure, and the solubility of the gas is only related to its own partial pressure. Under a certain pressure, as the water temperature increases, the partial pressure of water vapor increases, while the partial pressure of air and oxygen decreases. When the pressure on the water surface is lower than atmospheric pressure, the solubility of oxygen can also reach zero at lower water temperatures. In this way, oxygen molecules on the water surface are expelled or converted into other gases, resulting in zero partial pressure of oxygen. Oxygen in the water continuously escapes, achieving the effect of deoxygenation.

2、 Equipment composition:

The vacuum transformation of the deaerator mainly consists of the deaerator (with the deaeration head and deaeration water tank using existing equipment), water injection circulation box, water injection vacuum pump unit, water intake pump unit, etc.

When the deaerator is running, the deaeration water tank is in a negative pressure state. When installing at a high position, the distance between the outlet of the water tank and the inlet of the boiler feed pump should be relatively large, preferably not less than 10 meters; When installed at a low position, the outlet of the water tank is connected to the water intake pump unit to increase the pressure of the negative pressure water before entering the boiler feed pump. The water jet vacuum pump unit is equipped with a long throat water jet vacuum pump, which has a compact design structure and extremely low specific power consumption. And it has high suction efficiency, with a suction volume twice that of the old model under the same conditions. Very low noise level, no vibration, and simpler installation and layout.

3、 Operation method:

1. Fill the circulating water tank of the water jet vacuum pump unit with cooling water, start the centrifugal pump of the unit, and ensure that the working water pressure is ≥ 3.0kg/cm2. The water jet vacuum pump starts working, open the connecting valve between the water jet vacuum pump and the deoxygenation head.

2. After the vacuum degree of the deaerator stabilizes for a few minutes, turn on the liquid level automatic control alarm, and at this time, the deaerator inlet centrifugal pump and solenoid valve (water) will automatically start. Softened water enters the deaerator for deoxygenation, with an inlet pressure of ≥ 2kg/cm2.

3. After the deoxygenated water in the water tank rises to the medium water level, open the gate valve between the deoxygenation head of the deaerator and the water intake pump to remove the air in the water intake pump. Observe the vacuum gauge on the water intake pump to make it basically the same as the vacuum degree of the deoxygenation head.

4. Open the outlet valve of the deaerator water tank and fill the water intake pump with deoxygenated water (about a few minutes). At this time, the vacuum gauge reading at the inlet of the water intake pump is about 100mmHg lower than that of the deaerator.

5. Start the centrifugal pump of the water intake pump to circulate the water intake pump, with a pressure of about 3kg/cm2. If there is no pressure, it indicates that there is no water in the water pump or it is not filled with water. At this time, the above points 3 and 4 should be repeated.

6. Gradually open the outlet valve of the water intake pump, with a working pressure of ≥ 2kg/cm2, and simultaneously turn on the boiler feedwater pump to allow deoxygenated water to enter the boiler.

(1) For boilers with continuous water inflow, the inlet water volume should be adjusted by adjusting the outlet valve of the boiler feedwater pump. Due to continuous water inflow, the fluctuation of water inflow is not significant, which is more in line with the working state of the water intake pump. Therefore, this method should be used as much as possible when in use.

(2) For boilers with intermittent water intake, the water intake pump and boiler feed pump can be started or stopped simultaneously. If the boiler stops water intake for a short period of time, the water intake pump can continue to operate and cannot be stopped.

7. Sampling analysis of residual oxygen in deoxygenated water should be conducted every two hours during initial production. Based on the analysis results, the heat source flow rate of the softened water heating equipment should be adjusted to meet the temperature difference requirements.

Note: 1. Before operation, all valves should be in the closed state.

During the maintenance of the deaerator, the bypass valve of the softened water tank can be opened to allow the softened water to directly enter the boiler feedwater pump.

4、 Equipment features:

Compared with other deoxygenation methods, vacuum deoxygenation has the following advantages:

Vacuum deoxygenation can be carried out at low temperatures without consuming steam, allowing all the steam produced by the boiler to be used for production, thereby saving a lot of energy; Vacuum deoxygenation has a wider temperature range than thermal deoxygenation, and when the steam volume fluctuates greatly, it will not affect the deoxygenation effect and operate stably; The return water from the workshop can be used to increase the temperature of the water supply, without the need for heating equipment, with less one-time investment and less daily maintenance; Vacuum deoxygenation has better deoxygenation effect, which is significantly lower than the national standard.

 

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