Deaerator retrofit

1、 Current situation of deoxygenation equipment:

As the operation of the deaerator increases, power plant operators have found that the dissolved oxygen is not qualified and the energy consumption increases with the increase of exhaust volume during the use of the deaerator. There are differences in the working pressure of the deaerator water tank and deaerator head (the working pressure of the water tank is slightly higher than that of the deaerator head), and the operation is unstable. The deaerator head will show obvious vibration, and the dissolved oxygen in the effluent will exceed the standard (the national standard for low-pressure deaerators is 15 micrograms/liter), sometimes reaching 50 micrograms/liter. The long-term operating efficiency of the equipment is low, which affects the safe and economic operation of the main engine and boiler

2、 Problems with ordinary deaerators:

Deaerator is a device used to remove air and oxygen dissolved in water, and it is also a hybrid heat exchanger that has the functions of heating and storing boiler feedwater. The steam used for heating directly exchanges heat with the feedwater through sufficient contact in the deaerator, heating the feedwater to the saturation temperature at working pressure, causing non condensable gases in the deaerator to escape from the feedwater. The escaping gases carry a small amount of steam and are discharged through the exhaust outlet.

Among the widely used deaerator series in China, the rotary membrane thermal deaerator is one of them. The water is sprayed through the membrane holes onto the pipe wall, forming atomized water droplets during the downward process. Multiple layers of atomized water droplets overlap with each other and come into contact with the heating steam flowing upstream for preheating. Due to the large and uniform contact area, the water and steam can be fully mixed and heated, and some non condensable gases are released. The deaerator effect and heat transfer effect are better than those of the spray pan deaerator and the spray filler deaerator to a certain extent. However, there are still many problems with the operation of the rotary membrane deaerator

(1) Under rated operating conditions, it can generally meet the usage requirements, but it is difficult to achieve the intended deoxygenation effect under variable operating conditions (especially at low operating conditions).

(2) During operation, the pressure inside the deaerator has reached the rated working pressure, but the outlet temperature is lower than the saturation temperature under pressure, making it difficult for non condensable gases such as oxygen in the water to precipitate.

(3) In order to solve the problem in the second point, it is often necessary to increase the steam volume during operation, and the pressure of the deaerator will increase accordingly. In order to maintain the pressure of the deaerator, the upper exhaust port must increase the steam discharge volume, which wastes the steam source and is not conducive to energy conservation and consumption reduction.

(4) After running for a long time, the packing layer will deform, fall off, and compress under the impact of water vapor, losing operational elasticity, reducing the specific surface area of steam water heat exchange, and increasing steam water resistance, which will prevent the internal pressure of the deaerator from rising and deeply affect the deaeration effect.

(5) The water vapor heat exchange process is short, consumes a large amount of steam, is uneconomical, operates unstably, and has excessive oxygen content.

3、 Structure and performance of improved rotary film deaerator (patented technology):

1. Structure of improved rotary film deaerator:

The heat and mass transfer methods of the improved membrane tube of the rotary film deaerator are different from the existing liquid injection, atomization, and bubble boiling methods. The main difference is that the three heat transfer methods of jet passing through the rotary film and suspended bubble boiling are condensed into one heat and mass transfer method. It has high thermal efficiency, not only with great heat absorption function, but also with great analytical ability; Transforming the natural falling film into a strong and powerful film, increasing the renewal degree of the liquid film, and causing the liquid film to strongly rotate and suck up a large amount of steam along the pipe wall, enhancing heat and mass transfer functions. Changing the opposite phase bubble boiling to a suspended bubble boiling, increasing the overflow point (splashing) when the steam flow rate in the layer is high, and maintaining the vapor (gas) channel; Shrink three independent heat and mass transfer devices into one unit and complete it within a single component. Due to its high efficiency and certain special functions, it breaks through the technical performance of existing deaerators.

Through multiple experimental analyses and practical modifications, we have carried out multiple modifications to the internal components of the deaerator head of the rotary film thermal deaerator, and have developed specific implementation methods for the deaerator modification. After the modification of multiple deaerators in the power plant according to this plan, the deaeration effect was good. Our new type of water film deaerator (improved rotary film type) is a new structure deaerator researched and promoted in the past decade. It is designed to meet the needs of heating units and peak shaving units, and solve the efficiency problems of deaerator caused by high dissolved oxygen in the feedwater, low inlet water temperature, and frequent changes in operating conditions.

2. Performance of improved rotary film deaerator:

The improved rotary membrane deaerator is a new generation product of spray packing type and rotary membrane type. It combines the advantages of various deaerators and carries out deep optimization design. First, the exhaust baffle is changed into an efficient steam water separator, which greatly reduces the water carried in the exhaust and heat loss, and the exhaust volume is controlled below 1 ‰ (5 ‰ for spray, 3 ‰ for rotary membrane type).

The five stage deoxygenation principle of the new type of deaerator strictly ensures high deoxygenation efficiency during normal operation of the equipment. The dissolved oxygen content in the effluent of the low-pressure deaerator can be maintained below 15 micrograms/liter for a long time. At the same time, the surplus deoxygenation space allows the deaerator to operate significantly at overload (usually designed at 50% of the rated output, but can be designed separately according to requirements), or operate at low temperature (low pressure) inlet water (i.e. fully replenished water state operation).

The new type of deaerator has been operating in the market for nearly ten years, with more than one hundred reformed manufacturers and more than 500 sets of equipment in operation. It is recognized as a new generation of water spray pan type, spray type and rotary film type deaerator.

3. The main features of the improved rotary film deaerator are:

Stable operation, high deoxygenation efficiency, and good adaptability to load changes. In a short period of time (usually around half an hour), the dissolved oxygen content in the feedwater can reach the boiler water and steam quality standards (high pressure within 7 micrograms per liter, low pressure within 15 micrograms per liter). The requirements for water quality and temperature are not strict

4、 Technical analysis and comparison:

Comparison of performance with other forms of deaerators

5、 Transformation process and duration:

1. Remove the original deoxygenation head and replace it with an improved rotary film deoxygenation head, or remove the internal components of the original deoxygenation head and replace them with new ones

2. Connect the inlet and outlet pipelines of the original system according to the relevant layout requirements of the new deaerator

The project renovation period is about 5 days.

Attachment: Internal structure diagram of improved rotary film deaerator

6、 Expected effect after renovation:

1. The dissolved oxygen in the effluent can be controlled within the national standard range of ≤ 15 micrograms/liter;

2. Eliminate the pressure difference in the deaeration head water tank and abnormal vibration of the deaeration head during the operation of the original deaerator;

3. The steam water separation efficiency at the exhaust outlet has been reduced from the original exhaust volume of 3 ‰ to within 1 ‰, significantly improving the economy.

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